Patent Description:
Recent generation mobile telecommunication systems, such as those based on the 3GPP defined UMTS and Long Term Evolution (LTE) architectures, are able to support a wider range of services than simple voice and messaging services offered by previous generations of mobile telecommunication systems. In addition to supporting these kinds of more sophisticated services and devices, it is also proposed for newer generation mobile telecommunication systems to support less complex services and devices which make use of the reliable and wide ranging coverage of newer generation mobile telecommunication systems without necessarily needing to rely on the high data rates available in such systems.

Future wireless communications networks will therefore be expected to routinely and efficiently support communications with a wider range of devices associated with a wider range of data traffic profiles and types than current systems are optimised to support. For example it is expected future wireless communications networks will be expected to efficiently support communications with devices including reduced complexity devices, machine type communication (MTC) devices, high resolution video displays, virtual reality headsets and so on. Some of these different types of devices may be deployed in very large numbers, for example low complexity devices for supporting the "The Internet of Things", and may typically be associated with the transmissions of relatively small amounts of data with relatively high latency tolerance.

In view of this there is expected to be a desire for future wireless communications networks, for example those which may be referred to as <NUM> or new radio (NR) system / new radio access technology (RAT) systems, as well as future iterations / releases of existing systems, to efficiently support connectivity for a wide range of devices associated with different applications and different characteristic data traffic profiles.

As radio technologies continue to improve, for example with the development of <NUM>, the possibility arises for these technologies to be used not only by infrastructure equipment to provide service to wireless communications devices in a cell, but also for interconnecting infrastructure equipment to provide a wireless backhaul. In view of this there is a need to ensure that a donor infrastructure equipment that is physically connected to the core network does not suffer from a "capacity crunch" when a large amount of data is being transmitted from various communications devices and infrastructure equipment to the core network via the donor infrastructure equipment.

Non patent document "<NPL>) describes some issues that may influence IAB and potential enhancements to NR that can help improve the efficiency of the IAB backhaul.

Non patent document "<NPL>) presents some considerations on IAB physical layer technology enhancements according to the scenarios and topologies discussed in the prior art.

Non patent document "<NPL>) discusses specific use cases and scenarios for IAB which should be prioritized to be addressed along with corresponding enabling technology feature building blocks.

The present disclosure can help address or mitigate at least some of the issues discussed above as defined in the appended claims. The dependent claims define preferred embodiments of the invention. In the following, embodiments of the invention are described with particular reference to <FIG> and <FIG>. The other embodiments and/ or examples of the disclosure are provided for illustrative purposes to support a better understanding of the invention.

The network <NUM> includes a plurality of base stations <NUM> connected to a core network <NUM>. Each base station provides a coverage area <NUM> (i.e. a cell) within which data can be communicated to and from communications devices <NUM>.

Although each base station <NUM> is shown in <FIG> as a single entity, the skilled person will appreciate that some of the functions of the base station may be carried out by disparate, interconnected elements, such as antennas, remote radio heads, amplifiers, etc. Collectively, one or more base stations may form a radio access network.

Data is transmitted from base stations <NUM> to communications devices <NUM> within their respective coverage areas <NUM> via a radio downlink. Data is transmitted from communications devices <NUM> to the base stations <NUM> via a radio uplink. The core network <NUM> routes data to and from the communications devices <NUM> via the respective base stations <NUM> and provides functions such as authentication, mobility management, charging and so on. Terminal devices may also be referred to as mobile stations, user equipment (UE), user terminal, mobile radio, communications device, and so forth.

Services provided by the core network <NUM> may include connectivity to the internet or to external telephony services. The core network <NUM> may further track the location of the communications devices <NUM> so that it can efficiently contact (i.e. page) the communications devices <NUM> for transmitting downlink data towards the communications devices <NUM>.

Base stations, which are an example of network infrastructure equipment, may also be referred to as transceiver stations, nodeBs, e-nodeBs, eNB, g-nodeBs, gNB and so forth. In this regard different terminology is often associated with different generations of wireless telecommunications systems for elements providing broadly comparable functionality. However, certain embodiments of the disclosure may be equally implemented in different generations of wireless telecommunications systems, and for simplicity certain terminology may be used regardless of the underlying network architecture. That is to say, the use of a specific term in relation to certain example implementations is not intended to indicate these implementations are limited to a certain generation of network that may be most associated with that particular terminology.

An example configuration of a wireless communications network which uses some of the terminology proposed for NR and <NUM> is shown in <FIG>. A 3GPP Study Item (SI) on New Radio Access Technology (NR) has been defined [<NUM>]. In <FIG> a plurality of transmission and reception points (TRPs) <NUM> are connected to distributed control units (DUs) <NUM>, <NUM> by a connection interface represented as a line <NUM>. Each of the TRPs <NUM> is arranged to transmit and receive signals via a wireless access interface within a radio frequency bandwidth available to the wireless communications network. Thus within a range for performing radio communications via the wireless access interface, each of the TRPs <NUM>, forms a cell of the wireless communications network as represented by a circle <NUM>. As such, wireless communications devices <NUM> which are within a radio communications range provided by the cells <NUM> can transmit and receive signals to and from the TRPs <NUM> via the wireless access interface. Each of the distributed units <NUM>, <NUM> are connected to a central unit (CU) <NUM> (which may be referred to as a controlling node) via an interface <NUM>. The central unit <NUM> is then connected to the a core network <NUM> which may contain all other functions required to transmit data for communicating to and from the wireless communications devices and the core network <NUM> may be connected to other networks <NUM>.

The TRPs <NUM> of <FIG> may in part have a corresponding functionality to a base station or eNodeB of an LTE network. Similarly the communications devices <NUM> may have a functionality corresponding to the UE devices <NUM> known for operation with an LTE network. It will be appreciated therefore that operational aspects of a new RAT network (for example in relation to specific communication protocols and physical channels for communicating between different elements) may be different to those known from LTE or other known mobile telecommunications standards. However, it will also be appreciated that each of the core network component, base stations and communications devices of a new RAT network will be functionally similar to, respectively, the core network component, base stations and communications devices of an LTE wireless communications network.

In terms of broad top-level functionality, the core network <NUM> connected to the new RAT telecommunications system represented in <FIG> may be broadly considered to correspond with the core network <NUM> represented in <FIG>, and the respective central units <NUM> and their associated distributed units / TRPs <NUM> may be broadly considered to provide functionality corresponding to the base stations <NUM> of <FIG>. The term network infrastructure equipment / access node may be used to encompass these elements and more conventional base station type elements of wireless telecommunications systems. Depending on the application at hand the responsibility for scheduling transmissions which are scheduled on the radio interface between the respective distributed units and the communications devices may lie with the controlling node / central unit and / or the distributed units / TRPs. A communications device <NUM> is represented in <FIG> within the coverage area of the first communication cell <NUM>. This communications device <NUM> may thus exchange signalling with the first central unit <NUM> in the first communication cell <NUM> via one of the distributed units <NUM> associated with the first communication cell <NUM>.

It will further be appreciated that <FIG> represents merely one example of a proposed architecture for a new RAT based telecommunications system in which approaches in accordance with the principles described herein may be adopted, and the functionality disclosed herein may also be applied in respect of wireless telecommunications systems having different architectures.

Thus certain embodiments of the disclosure as discussed herein may be implemented in wireless telecommunication systems / networks according to various different architectures, such as the example architectures shown in <FIG> and <FIG>. It will thus be appreciated the specific wireless telecommunications architecture in any given implementation is not of primary significance to the principles described herein. In this regard, certain embodiments of the disclosure may be described generally in the context of communications between network infrastructure equipment / access nodes and a communications device, wherein the specific nature of the network infrastructure equipment / access node and the communications device will depend on the network infrastructure for the implementation at hand. For example, in some scenarios the network infrastructure equipment / access node may comprise a base station, such as an LTE-type base station <NUM> as shown in <FIG> which is adapted to provide functionality in accordance with the principles described herein, and in other examples the network infrastructure equipment may comprise a control unit / controlling node <NUM> and / or a TRP <NUM> of the kind shown in <FIG> which is adapted to provide functionality in accordance with the principles described herein.

A more detailed diagram of some of the components of the network shown in <FIG> is provided by <FIG>. In <FIG>, a TRP <NUM> as shown in <FIG> comprises, as a simplified representation, a wireless transmitter <NUM>, a wireless receiver <NUM> and a controller or controlling processor <NUM> which may operate to control the transmitter <NUM> and the wireless receiver <NUM> to transmit and receive radio signals to one or more UEs <NUM> within a cell <NUM> formed by the TRP <NUM>. As shown in <FIG>, an example UE <NUM> is shown to include a corresponding transmitter <NUM>, a receiver <NUM> and a controller <NUM> which is configured to control the transmitter <NUM> and the receiver <NUM> to transmit signals representing uplink data to the wireless communications network via the wireless access interface formed by the TRP <NUM> and to receive downlink data as signals transmitted by the transmitter <NUM> and received by the receiver <NUM> in accordance with the conventional operation.

The transmitters <NUM>, <NUM>, the receivers <NUM>, <NUM> may include radio frequency filters and amplifiers as well as signal processing components and devices in order to transmit and receive radio signals in accordance for example with the <NUM>/NR standard. The controllers <NUM>, <NUM> may be, for example, a microprocessor, a CPU, or a dedicated chipset, etc., configured to carry out instructions which are stored on a computer readable medium, such as a non-volatile memory. The processing steps described herein may be carried out by, for example, a microprocessor in conjunction with a random access memory, operating according to instructions stored on a computer readable medium.

As shown in <FIG>, the TRP <NUM> also includes a network interface <NUM> which connects to the DU <NUM> via a physical interface <NUM>. The network interface <NUM> therefore provides a communication link for data and signalling traffic from the TRP <NUM> via the DU <NUM> and the CU <NUM> to the core network <NUM>.

The interface <NUM> between the DU <NUM> and the CU <NUM> is known as the F1 interface which can be a physical or a logical interface. The F1 interface <NUM> between CU and DU may operate in accordance with specifications 3GPP TS <NUM> and 3GPP TS <NUM>, and may be formed from a fibre optic or other wired high bandwidth connection. In one example the connection <NUM> from the TRP <NUM> to the DU <NUM> is via fibre optic. The connection between a TRP <NUM> and the core network <NUM> can be generally referred to as a backhaul, which comprises the interface <NUM> from the network interface <NUM> of the TRP10 to the DU <NUM> and the F1 interface <NUM> from the DU <NUM> to the CU <NUM>.

Example arrangements of the present technique can be formed from a wireless communications network corresponding to that shown in <FIG> or <FIG>, as shown in <FIG> provides an example in which cells of a wireless communications network are formed from infrastructure equipment which are provided with an Integrated Access and Backhaul (IAB) capability. The wireless communications network <NUM> comprises the core network <NUM> and a first, a second, a third and a fourth communications device (respectively <NUM>, <NUM>, <NUM> and <NUM>) which may broadly correspond to the communications devices <NUM>, <NUM> described above.

The wireless communications network <NUM> comprises a radio access network, comprising a first infrastructure equipment <NUM>, a second infrastructure equipment <NUM>, a third infrastructure equipment <NUM>, and a fourth infrastructure equipment <NUM>. Each of the infrastructure equipment provides a coverage area (i.e. a cell, not shown in <FIG>) within which data can be communicated to and from the communications devices <NUM> to <NUM>. For example, the fourth infrastructure equipment <NUM> provides a cell in which the third and fourth communications devices <NUM> and <NUM> may obtain service. Data is transmitted from the fourth infrastructure equipment <NUM> to the fourth communications device <NUM> within its respective coverage area (not shown) via a radio downlink. Data is transmitted from the fourth communications device <NUM> to the fourth infrastructure equipment <NUM> via a radio uplink.

The infrastructure equipment <NUM> to <NUM> in <FIG> may correspond broadly to the TRPs <NUM> of <FIG> and <FIG>.

The first infrastructure equipment <NUM> in <FIG> is connected to the core network <NUM> by means of one or a series of physical connections. The first infrastructure equipment <NUM> may comprise the TRP <NUM> (having the physical connection <NUM> to the DU <NUM>) in combination with the DU <NUM> (having a physical connection to the CU <NUM> by means of the F1 interface <NUM>) and the CU <NUM> (being connected by means of a physical connection to the core network <NUM>).

However, there is no direct physical connection between any of the second infrastructure equipment <NUM>, the third infrastructure equipment <NUM>, and the fourth infrastructure equipment <NUM> and the core network <NUM>. As such, it may be necessary (or, otherwise determined to be appropriate) for data received from a communications device (i.e. uplink data), or data for transmission to a communications device (i.e. downlink data) to be transmitted to or from the core network <NUM> via other infrastructure equipment (such as the first infrastructure equipment <NUM>) which has a physical connection to the core network <NUM>, even if the communications device is not currently served by the first infrastructure equipment <NUM> but is, for example, in the case of the wireless communications device <NUM>, served by the fourth infrastructure equipment <NUM>.

The second, third and fourth infrastructure equipment <NUM> to <NUM> in <FIG> may each comprise a TRP, broadly similar in functionality to the TRPs <NUM> of <FIG>.

In some arrangements of the present technique, one or more of the second to fourth infrastructure equipment <NUM> to <NUM> in <FIG> may further comprise a DU <NUM>, and in some arrangements of the present technique, one or more of the second to fourth infrastructure equipment <NUM> to <NUM> may comprise a DU and a CU.

In some arrangements of the present technique, the CU <NUM> associated with the first infrastructure equipment <NUM> may perform the function of a CU not only in respect of the first infrastructure equipment <NUM>, but also in respect of one or more of the second, the third and the fourth infrastructure equipment <NUM> to <NUM>.

In order to provide the transmission of the uplink data or the downlink data between a communications device and the core network, a route is determined by any suitable means, with one end of the route being an infrastructure equipment physically connected to a core network and by which uplink and downlink traffic is routed to or from the core network.

In the following, the term 'node' is used to refer to an entity or infrastructure equipment which forms a part of a route for the transmission of the uplink data or the downlink data.

An infrastructure equipment which is physically connected to the core network and operated in accordance with an example arrangement may provide communications resources to other infrastructure equipment and so is referred to as a 'donor node'. An infrastructure equipment which acts as an intermediate node (i.e. one which forms a part of the route but is not acting as a donor node) is referred to as a 'relay node'. It should be noted that although such intermediate node infrastructure equipment act as relay nodes on the backhaul link, they may also provide service to communications devices. The relay node at the end of the route which is the infrastructure equipment controlling the cell in which the communications device is obtaining service is referred to as an 'end node'.

In the wireless network illustrated in <FIG>, each of the first to fourth infrastructure equipment <NUM> to <NUM> may therefore function as nodes. For example, a route for the transmission of uplink data from the fourth communications device <NUM> may consist of the fourth infrastructure equipment <NUM> (acting as the end node), the third infrastructure equipment <NUM> (acting as a relay node), and the first infrastructure equipment <NUM> (acting as the donor node). The first infrastructure <NUM>, being connected to the core network <NUM>, transmits the uplink data to the core network <NUM>.

For clarity and conciseness in the following description, the first infrastructure equipment <NUM> is referred to below as the 'donor node', the second infrastructure equipment <NUM> is referred to below as 'Node <NUM>', the third infrastructure equipment <NUM> is referred to below as 'Node <NUM>' and the fourth infrastructure equipment <NUM> is referred to below as 'Node <NUM>'.

For the purposes of the present disclosure, the term 'upstream node' is used to refer to a node acting as a relay node or a donor node in a route, which is a next hop when used for the transmission of data via that route from a wireless communications device to a core network. Similarly, 'downstream node' is used to refer to a relay node from which uplink data is received for transmission to a core network. For example, if uplink data is transmitted via a route comprising (in order) the Node <NUM><NUM>, the Node <NUM><NUM> and the donor node <NUM>, then the donor node <NUM> is an upstream node with respect to the Node <NUM><NUM>, and the Node <NUM><NUM> is a downstream node with respect to the Node <NUM><NUM>.

More than one route may be used for the transmission of the uplink data from a given communications device; this is referred to herein as 'multi-connectivity'. For example, the uplink data transmitted by the wireless communications device <NUM> may be transmitted either via the Node <NUM><NUM> and the Node <NUM><NUM> to the donor node <NUM>, or via the Node <NUM><NUM> and the Node <NUM><NUM> to the donor node <NUM>.

In the following description, example arrangements are described in which each of the nodes is an infrastructure equipment; the present disclosure is not so limited. A node may comprise at least a transmitter, a receiver and a controller. In some arrangements of the present technique, the functionality of a node (other than the donor node) may be carried out by a communications device, which may be the communications device <NUM> (of <FIG>) or <NUM> (of <FIG>), adapted accordingly. As such, in some arrangements of the present technique, a route may comprise one or more communications devices. In other arrangements, a route may consist of only a plurality of infrastructure equipment.

In some arrangements of the present technique, an infrastructure equipment acting as a node may not provide a wireless access interface for the transmission of data to or by a communications device other than as part of an intermediate transmission along a route.

In some arrangements of the present technique, a route is defined considering a wireless communications device (such as the wireless communications device <NUM>) as the start of a route. In other arrangements a route is considered to start at an infrastructure equipment which provides a wireless access interface for the transmission of the uplink data by a wireless communications device.

Each of the first infrastructure equipment acting as the donor node <NUM> and the second to fourth infrastructure equipment acting as the Nodes <NUM>-<NUM><NUM>-<NUM> may communicate with one or more other nodes by means of an inter-node wireless communications link, which may also be referred to as a wireless backhaul communications links. For example, <FIG> illustrates four inter-node wireless communications links <NUM>, <NUM>, <NUM>, <NUM>.

Each of the inter-node wireless communications links <NUM>, <NUM>, <NUM>, <NUM> may be provided by means of a respective wireless access interface. Alternatively, two or more of the inter-node wireless communications links <NUM>, <NUM>, <NUM>, <NUM> may be provided by means of a common wireless access interface and in particular, in some arrangements of the present technique, all of the inter-node wireless communications links <NUM>, <NUM>, <NUM>, <NUM> are provided by a shared wireless access interface.

A wireless access interface which provides an inter-node wireless communications link may also be used for communications between an infrastructure equipment (which may be a node) and a communications device which is served by the infrastructure equipment. For example, the fourth wireless communications device <NUM> may communicate with the infrastructure equipment Node <NUM><NUM> using the wireless access interface which provides the inter-node wireless communications link <NUM> connecting the Node <NUM><NUM> and the Node <NUM><NUM>.

The wireless access interface(s) providing the inter-node wireless communications links <NUM>, <NUM>, <NUM>, <NUM> may operate according to any appropriate specifications and techniques. In some arrangements of the present technique, a wireless access interface used for the transmission of data from one node to another uses a first technique and a wireless access interface used for the transmission of data between an infrastructure equipment acting as a node and a communications device may use a second technique different from the first. In some arrangements of the present technique, the wireless access interface(s) used for the transmission of data from one node to another and the wireless access interface(s) used for the transmission of data between an infrastructure equipment and a communications device use the same technique.

Examples of wireless access interface standards include the third generation partnership project (3GPP)-specified GPRS/EDGE ("<NUM>"), WCDMA (UMTS) and related standards such as HSPA and HSPA+ ("<NUM>"), LTE and related standards including LTE-A ("<NUM>"), and NR ("<NUM>"). Techniques that may be used to provide a wireless access interface include one or more of TDMA, FDMA, OFDMA, SC-FDMA, CDMA. Duplexing (i.e. the transmission over a wireless link in two directions) may be by means of frequency division duplexing (FDD) or time division duplexing (TDD) or a combination of both.

In some arrangements of the present technique, two or more of the inter-node wireless communications links <NUM>, <NUM>, <NUM>, <NUM> may share communications resources. This may be because two or more of the inter-node wireless communications links <NUM>, <NUM>, <NUM>, <NUM> are provided by means of a single wireless access interface or because two or more of the inter-node wireless communications links <NUM>, <NUM>, <NUM>, <NUM> nevertheless operate simultaneously using a common range of frequencies.

The nature of the inter-node wireless communications links <NUM>, <NUM>, <NUM>, <NUM> may depend on the architecture by which the wireless backhaul functionality is achieved.

A new study item on Integrated Access and Backhaul for NR [<NUM>] has been approved. Several requirements and aspects for the integrated access and wireless backhaul for NR to address are discussed in [<NUM>], which include:.

The stated objective of the study detailed in [<NUM>] is to identify and evaluate potential solutions for topology management for single-hop/multi-hop and redundant connectivity, route selection and optimisation, dynamic resource allocation between the backhaul and access links, and achieving high spectral efficiency while also supporting reliable transmission.

<FIG> shows the scenario presented in [<NUM>], where a backhaul link is provided from cell site A <NUM> to cells B <NUM> and C <NUM> over the air. It is assumed that cells B <NUM> and C <NUM> have no wired backhaul connectivity. Considering the CU/DU split architecture in NR as described above, it can be assumed that all of cells A <NUM>, B <NUM> and C <NUM> have a dedicated DU unit and are controlled by the same CU.

Several architecture requirements for IAB are laid out in [<NUM>]. These include the support for multiple backhaul hops, that topology adaptation for physically fixed relays shall be supported to enable robust operation, minimisation of impact to core network specifications, consideration of impact to core networking signalling load, and Release <NUM> NR specifications should be reused as much as possible in the design of the backhaul link, with enhancements considered.

<FIG> is reproduced from [<NUM>], and shows an example of a wireless communications system comprising a plurality of IAB-enabled nodes, which may for example be TRPs forming part of an NR network. These comprise an IAB donor node <NUM> which has a connection to the core network, two IAB nodes (a first IAB node <NUM> and a second IAB node <NUM>) which have backhaul connections to the IAB donor node <NUM>, and a third IAB node <NUM> (or end IAB node) which has a backhaul connection to each of the first IAB node <NUM> and the second IAB node <NUM>. Each of the first IAB node <NUM> and third IAB node <NUM> have wireless access connections to UEs <NUM> and <NUM> respectively. As shown in <FIG>, originally the third IAB node <NUM> may communicate with the IAB donor node <NUM> via the first IAB node <NUM>. After the second IAB node <NUM> emerges, there are now two candidate routes from the third IAB node <NUM> to the IAB donor node <NUM>; via the first IAB node <NUM> and via the new second IAB node <NUM>. The new candidate route via the second IAB node <NUM> will play an important role when there is a blockage in the first IAB node <NUM> to IAB donor node <NUM> link. Hence, knowing how to manage the candidate routes efficiently and effectively is important to ensure timely data transmission between relay nodes, especially when considering the characteristics of wireless links.

Various architectures have been proposed in order to provide the IAB functionality. The below described embodiments of the present technique are not restricted to a particular architecture. However, a number of candidate architectures which have been considered in, for example, 3GPP document [<NUM>] are described below.

<FIG> illustrates one possible architecture by which the donor Node <NUM>, the Node <NUM><NUM> and the Node <NUM><NUM> may provide a wireless backhaul to provide connectivity for the UEs <NUM>, <NUM>, <NUM>.

In <FIG>, each of the infrastructure equipment acting as an IAB nodes <NUM>, <NUM> and the donor node <NUM>, includes a distributed unit (DU) <NUM>, <NUM>, <NUM> which communicates with the UEs <NUM>, <NUM>, <NUM> and (in the case of the DUs <NUM>, <NUM> associated with the donor node <NUM> and the Node <NUM><NUM>) with the respective downstream IAB nodes <NUM>, <NUM>. Each of the IAB nodes <NUM>, <NUM> (not including the donor node <NUM>) includes a mobile terminal (MT) <NUM>, <NUM>, which includes a transmitter and receiver (not shown) for transmitting and receiving data to and from the DU of an upstream IAB node and an associated controller (not shown). The inter-node wireless communications links <NUM>, <NUM> may be in the form of new radio (NR) "Uu" wireless interface. The mobile terminals <NUM>, <NUM> may have substantially the same functionality as a UE, at least at the access stratum (AS) layer. Notably, however, an MT may not have an associated subscriber identity module (SIM) application; a UE may be conventionally considered to be the combination of an MT and a SIM application.

The Uu wireless interfaces used by IAB nodes to communicate with each other may also be used by UEs to transmit and receive data to and from the DU of the upstream IAB node. For example, the Uu interface <NUM> which is used by the Node <NUM><NUM> for communication with the donor node <NUM> may also be used by the UE <NUM> to transmit and receive data to and from the donor node <NUM>.

Similarly, an end node (such as the Node <NUM><NUM>) may provide a Uu wireless interface <NUM> for the fourth UE <NUM> to communicate with the DU <NUM> of the Node <NUM><NUM>.

Alternative candidate architectures for the provision of IAB are provided in <FIG>. In both <FIG>, each IAB node includes a gNB function, providing a wireless access interface for the use of downstream IAB nodes and wireless communications devices. <FIG> differs from <FIG> in that, in <FIG>, PDU sessions are connected end-on-end to form the wireless backhaul; in <FIG>, PDU sessions are encapsulated so that each IAB node may establish an end-to-end PDU session which terminates at the IAB donor node <NUM>.

Given the vulnerable characteristics of wireless links, and considering multi-hops on the backhaul link, topology adaptation should be considered in the case that blockages or congestion occur in the backhaul link considering a given hop. It is therefore imperative to maximise the spectral efficiency of the backhaul link in order to maximise its capacity. Embodiments of the present technique seek to address how the capacity of the backhaul link can be increased.

In <FIG>, only the IAB Donor gNB <NUM> has a fixed line backhaul into the core network. It should be assumed in this case that the traffic from all the UEs <NUM> within the third IAB node's <NUM> coverage is backhauled firstly to the first IAB node <NUM>. This backhaul link must compete for capacity on the component carrier serving the first IAB Node <NUM> with all the UEs <NUM> within the coverage area of the first IAB Node <NUM>. In the relevant art, the first IAB Node <NUM> in such a system as that of <FIG> is called a "hop" - it relays communications between the end (third) IAB node <NUM> and the donor IAB node <NUM>. The backhaul link to the first IAB Node <NUM> requires enough capacity to support the traffic from all the UEs <NUM>, bearing in mind that some of these may have stringent QoS requirements that translate into high traffic intensities.

Even more challenging is that the last hop in the backhaul link, such as that between the first IAB Node <NUM> and the IAB Donor node <NUM> now has even more stringent capacity needs since it has to backhaul UE traffic from both groups of UEs <NUM> and <NUM>. Embodiments of the present technique are directed to increasing as much as possible the spectral efficiency in the use of the limited radio resources assigned for backhaul, so as to mitigate the capacity crunch on the IAB backhaul.

<FIG> shows a part schematic, part message flow diagram of communications in a wireless communications network <NUM> in accordance with embodiments of the present technique. The wireless communications network <NUM> comprises a plurality of infrastructure equipment <NUM>, <NUM>, <NUM>, <NUM> each being configured to communicate with one or more others of the infrastructure equipment <NUM>, <NUM>, <NUM>, <NUM> via a backhaul communications link <NUM>, one or more of the infrastructure equipment <NUM>, <NUM>, <NUM>, <NUM> each being configured to communicate with one or more communications devices <NUM> via an access link <NUM>. A first of the infrastructure equipment <NUM> is configured to act as a donor node connected to a core network part <NUM> of the wireless communications network <NUM> and comprises transceiver circuitry 1002a and controller circuitry 1002b configured in combination to receive <NUM>, at the first infrastructure equipment <NUM>, signals representing data from one or more others of the infrastructure equipment <NUM>, <NUM>, <NUM> the data having been received at the one or more others of the infrastructure equipment <NUM>, <NUM>, <NUM> from one or more of the communications devices <NUM> or from other infrastructure equipment <NUM>, <NUM>, <NUM>, and to transmit <NUM>, by the first infrastructure equipment <NUM>, the data from the one or more others of the infrastructure equipment <NUM>, <NUM>, <NUM> to the core network part <NUM> of the wireless communications network <NUM>, wherein at least one of the infrastructure equipment <NUM>, <NUM>, <NUM>, <NUM> is configured to use at least one spectral efficiency enhancing technique to receive the signals, the at least one spectral efficiency enhancing technique allowing the at least one infrastructure equipment <NUM>, <NUM>, <NUM>, <NUM> to receive the signals in the backhaul communications link, the at least one spectral efficiency enhancing technique not allowing the at least one infrastructure equipment <NUM>, <NUM>, <NUM>, <NUM> to receive the signals in the access link.

All of the IAB relay nodes shown in <FIG> (such as the third IAB Node <NUM>), the hop nodes (such as the first IAB Node <NUM>) and donor nodes (e.g. node <NUM>) are gNBs that are physically fixed and not moving. It is therefore expected that the backhaul link between the end node and the hop or donor nodes would essentially be fixed. Such fixed links may potentially have a line of sight (LoS) as well. As the link is fixed, propagation conditions can be significantly improved by use of beam forming. Beam forming focuses all the power of the signal in a thin beam to maximize its directivity. In other words, the at least one spectral efficiency enhancing technique comprises receiving the signals using one or more beams, beam-formed specifically for the purpose, in which power of each of the signals is focussed, each of the one or more beams being separately identifiable and forming a directional bias with respect to the at least one infrastructure equipment.

In this arrangement, the fact that the beam forming increases the transmitter directivity and so reduces the impact of free space loss is exploited, leading to a high signal to interference and noise power ratio (SINR) at the IAB backhaul link receiver. In this arrangement, a high order modulation and coding scheme (MCS) that incorporates higher order modulation schemes such as <NUM>m-QAM where m has a value of <NUM> or more and higher Forward Error Code (FEC) code rates are used for such links. With such MCS with <NUM>m-QAM modulation and r code rate, each resource element (RE) allocated to the backhaul link will carry as many as rm information bits, increasing proportionately as either m or r is increased and so maximize the spectral efficiency of the backhaul because of the benign propagation conditions. In other words, the data may be modulated onto the signals with a higher order modulation scheme than if the at least one spectral efficiency enhancing technique was not used to receive the signals. The signals may be transmitted with a higher code rate than if the at least one spectral efficiency enhancing technique was not used to receive the signals.

In accordance with the invention as defined by the appended claims, spectral efficiency of the backhaul link especially from one hop to the next is improved by increasing the size of transmission resources that can be allocated in a resource allocation event. This is achieved through slot aggregation. In other words, the at least one spectral efficiency enhancing technique comprises transmitting, by the at least one infrastructure equipment to the one or more other infrastructure equipment, an indication that the one or more other infrastructure equipment may allocate a larger amount of radio resources for the backhaul communications link than compared to the radio resources for the access link, the larger amount of radio resources being allocated by aggregating a plurality of smaller units of radio resources.

Slot aggregation builds bigger transmission slots comprised of a plurality of slots. For example, while a normal slot may be configured as comprised of a certain number of subcarriers (e.g. <NUM> subcarriers) over N symbols, an aggregated slot in Rel <NUM> NR may comprise <NUM>, <NUM>, or <NUM> such normal slots and so lasts for 2N, 4N, or 8N symbols as the case may be. In Rel <NUM> NR, a slot in a time domain consists of <NUM> symbols (i.e. N = <NUM>). Slot aggregation allows the carriage of larger transmission blocks, thereby saving the resources that may have been used for, say, the multiple slot header information of the aggregated normal slots such as the PDCCH and a group-common PDCCH conveying a slot format information (SFI) etc. to be used for the traffic channels, further maximizing the spectral efficiency. Rel <NUM> NR allows slot aggregation only for the down-link (DL). The invention also includes performing slot aggregation on the up-link (UL) since the capacity crunch on the backhaul link is present both for the DL and the UL.

Furthermore, in accordance with the invention as defined by the appended claims, it is proposed that different slot aggregation factors are configured for the DL and the UL. For example, in a session when a UE connected to the end node is streaming video from the Internet, the DL traffic flow is more intensive than the UL traffic flow which in this case may simply be made up of interactive commands such as PAUSE, PLAY etc. In this example, the down backhaul link (donor to hop or end node) could be configured to use a higher slot aggregation factor of <NUM> while the up backhaul link (end node to hop or donor node) could be configured to use a lower slot aggregation factor of <NUM>. The situation could be reversed with a lower aggregation factor for the DL than the UL in sessions in which the said UE is uploading video clips to a website for example. Furthermore, the configurable number of aggregated slots can be increased for the down backhaul link and the up backhaul link. For example, while the configurable number of aggregated slots for conventional downlink (i.e. access link) is chosen from a list comprising {<NUM>, <NUM>, <NUM>}, the list of configurable number of slots for the down/up backhaul link can be different and include larger numbers for example {<NUM>,<NUM>,<NUM>,<NUM>}. Limiting to not more than <NUM> entries allows the same number of signalling bits to be used both for the access and backhaul links. The list can be made longer such as {<NUM>,<NUM>,<NUM>,<NUM>,<NUM>,<NUM>,<NUM>,<NUM>}. However, this requires an increase of one bit in the configuration signalling field. With an extended or new list for configuring the aggregation factor of the backhaul link, larger aggregation factors are made available for configuring the backhaul link.

In another arrangement, the fact that the highly directive signal produced by a technique such as beam forming results in very little multipath at the receiver is exploited. Furthermore, the stationarity of both the transmitter and receiver at each end of the backhaul link also means that there is very little time variation to the power of the signal at the antenna of the receiver. This arrangement exploits the low frequency selectivity (due to the reduced multipath) and the lack of time variation on the channel to reduce the density of the reference symbols such as sounding reference signals (SRS) or demodulation reference signals (DM-RS) transmitted for use in channel estimation for a physical channel (for example, a physical downlink shared channel (PDSCH) and a physical uplink shared channel (PUSCH)) in the backhaul link. In other words, the at least one spectral efficiency enhancing technique comprises transmitting the signals by the one or more others of the infrastructure equipment and/or the one or more of the communications devices with a smaller density DM-RS in the frequency domain on the backhaul communications link than compared to on the access link.

For example, if the DM-RS frequency domain density for the access link is <NUM> in <NUM> subcarriers and compared to the access link, the multipath delay spread is halved on the backhaul link, then the DM-RS frequency domain density can be reduced by half to <NUM> in <NUM> subcarriers for the backhaul link. Rel-<NUM> NR defines two configurable DM-RS densities for the access link: <NUM> in <NUM> and <NUM> in <NUM> subcarriers in the frequency domain. Lower densities will be defined for the backhaul such as <NUM> in N<NUM> and <NUM> in N<NUM> where N<NUM>= <NUM> and N<NUM>= <NUM> where K is a small integer. In addition, lower densities will be defined such as <NUM> in <NUM> subcarriers where K is a small integer (i.e. <NUM> in K resource block). The density of DM-RS determines the maximum number of layers for MIMO (spatial) multiplexing. The reduced density can be exploited to increase the number of spatial layers in the backhaul links. In other words, the at least one spectral efficiency enhancing technique comprises increasing a maximum number of layers onto which the signals can be multiplexed in the backhaul links using a multiple-input and multiple-output, MIMO, multiplexing process. In the current 3GPP specifications, where DM-RS densities can be configured to be <NUM> in <NUM> or <NUM> in <NUM>, the maximum layers are <NUM> and <NUM> respectively. Therefore when the lower densities are configured for backhaul link, the maximum layers can be increased. For example, when DM-RS density is <NUM> in X subcarriers, the maximum layers can be 2X. The DM-RS density on the backhaul link in the frequency domain can be fixed to the lowest density from a plurality of predefined, configurable densities on the access link.

Further, slot aggregation produces long slots with many DM-RS in the time domain. This arrangement also benefits from the low time variation in the channel to reduce the time domain density of DM-RS. In Rel-<NUM> NR, the number of positions for DL time domain DM-RS can be <NUM>, <NUM>, <NUM> and <NUM> within <NUM> slot (<NUM> symbols). In other words, the at least one spectral efficiency enhancing technique comprises transmitting the signals by the one or more others of the infrastructure equipment with a smaller density of demodulation reference signals, DM-RS, in the time domain on the backhaul communications link than compared to on the access link. In this arrangement and taking into account increased slot aggregation, the configurable number of positions can be restricted to only <NUM> for backhaul link (i.e. RRC parameter "DL-DMRS-add-pos" can be configured with only <NUM>). Furthermore, while DM-RS for the access link in the Rel <NUM> NR is mapped in every slot even in the case of the slot aggregation, DM-RS for backhaul link with slot aggregation can be reduced in time domain. For example, when Y slots are aggregated for backhaul link, the number of positions for time domain DM-RS can be less than Y (e.g. <NUM>) within Y aggregated slots. The number of positions can be implicitly determined by the number of aggregated slots or can be explicitly signalled for example, via an RRC parameter and/or a downlink control information (DCI) which is conveyed by PDCCH. The DM-RS density on the backhaul link in the time domain can also be fixed to the lowest density from a plurality of pre-defined, configurable densities available for use in the access link. This has the advantage of limiting changes in the Rel <NUM> signalling.

The above described arrangements - especially the ones related to DM-RS density reduction are based on orthogonal frequency or orthogonal time IAB-access resource partitioning schemes between backhaul and access links such as TDM and FDM in the same specific resource such as a component carrier (CC) or a bandwidth part (BWP). The DM-RS density reduction arrangements may be not suitable for space division multiplexing (SDM) schemes such as MU-MIMO in which SDM is applied between access and backhaul. In other words, radio resources for the backhaul link and radio resources for the access link may be separated from one another in either or both of the time domain and the frequency domain. The above described arrangements may also be applied to SDM. Resources may be preferentially allocated for the backhaul link over the access link.

<FIG> shows a flow diagram illustrating a process of communications in a communications system in accordance with embodiments of the present technique. The process shown by <FIG> is a method of controlling communications within a wireless communications network comprising a plurality of infrastructure equipment each being configured to communicate with one or more others of the infrastructure equipment via a backhaul communications link, one or more of the infrastructure equipment each being configured to communicate with one or more communications devices via an access link.

The method begins in step S1101. The method comprises, in step S1102, receiving, at a first of the infrastructure equipment acting as a donor node connected to a core network part of the wireless communications network, signals representing data from one or more others of the infrastructure equipment, the data having been received at the one or more others of the infrastructure equipment from one or more of the communications devices or from other infrastructure equipment. At least one of the infrastructure equipment uses at least one spectral efficiency enhancing technique to receive the signals, the at least one spectral efficiency enhancing technique allowing the at least one infrastructure equipment to receive the signals in the backhaul communications link, the at least one spectral efficiency enhancing technique not allowing the at least one infrastructure equipment to receive the signals in the access link. The process proceeds to step S1104, which comprises t transmitting, by the first infrastructure equipment, the data from the one or more others of the infrastructure equipment to the core network part of the wireless communications network. The process ends in step S1106.

Those skilled in the art would appreciate that the method shown by <FIG> may be adapted in accordance with embodiments of the present technique. For example, other intermediate steps may be included in the method, or the steps may be performed in any logical order. In particular, the at least one spectral efficiency enhancing technique used for communication between the donor node and the one or more others of the infrastructure equipment would have been originally configured for use during the initial setup of the backhaul link either when the downstream node was originally turned on or when the current session started or as part of radio link adaptation process. The at least one spectral efficiency enhancing technique may be used for the links between any two infrastructure equipment in the wireless communications network. For example, this may be between the donor node and end node, donor node and a hop (relay) node, two hop nodes, or a hop node and end node.

Though embodiments of the present technique have been described largely by way of the example system shown in <FIG>, it would be clear to those skilled in the art that they could be equally applied to other systems, where for example there may be many more nodes or paths to choose from, or more hops between the donor and end nodes.

Those skilled in the art would also appreciate that such infrastructure equipment and/or wireless communications networks as herein defined may be further defined in accordance with the various arrangements and embodiments discussed in the preceding paragraphs. It would be further appreciated by those skilled in the art that such infrastructure equipment and wireless communications networks as herein defined and described may form part of communications systems other than those defined by the present invention.

Claim 1:
A method performed by a first infrastructure equipment (<NUM>) forming part of a wireless communications network (<NUM>) comprising a plurality of other infrastructure equipment (<NUM>, <NUM>, <NUM>), the first infrastructure equipment and the plurality of other infrastructure equipment each being configured to communicate with one or more others of the infrastructure equipment via a backhaul communications link (<NUM>), one or more of the infrastructure equipment each being configured to communicate with one or more communications devices (<NUM>) via an access link (<NUM>), wherein the first infrastructure equipment is configured to act as a donor node connected to a core network part (<NUM>) of the wireless communications network, the method comprising
receiving (<NUM>), at the first infrastructure equipment, signals representing data from one or more others of the infrastructure equipment, the data having been received at the one or more others of the infrastructure equipment from one or more of the communications devices or from other infrastructure equipment, and
transmitting (<NUM>), by the first infrastructure equipment, the data from the one or more others of the infrastructure equipment to the core network part of the wireless communications network,
wherein the first infrastructure equipment uses at least one spectral efficiency enhancing technique to receive the signals, the at least one spectral efficiency enhancing technique allowing the first infrastructure equipment to receive the signals in the backhaul communications link, the at least one spectral efficiency enhancing technique not allowing the first infrastructure equipment to receive the signals in the access link,
wherein the at least one spectral efficiency enhancing technique comprises transmitting, by the first infrastructure equipment to the one or more other infrastructure equipment, an indication that the one or more other infrastructure equipment may allocate a larger amount of radio resources for the backhaul communications link than compared to the radio resources for the access link, the larger amount of radio resources being allocated by aggregating a plurality of smaller units of radio resources on downlink and uplink of the backhaul communications link between the first infrastructure equipment and the one or more other infrastructure equipment, wherein the slot aggregation factors on the downlink and the uplink of the backhaul communications link are different.