BACKGROUND Field of Disclosure

The present disclosure relates to methods and apparatus for the communication of signals between various infrastructure equipment, communications devices and a core network.

The present disclosure claims the Paris convention priority from European patent application number 20172558.7 the contents of which are incorporated by reference in their entirety.

Description of Related Art

The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.

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. For example, with the improved radio interface and enhanced data rates provided by LTE systems, a user is able to enjoy high data rate applications such as mobile video streaming and mobile video conferencing that would previously only have been available via a fixed line data connection. 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. The demand to deploy such networks is therefore strong and the coverage area of these networks, i.e. geographic locations where access to the networks is possible, may be expected to increase ever more rapidly.

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 5G 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 5G, 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 links between various infrastructure equipment in the backhaul are both stable and reliable, particularly where an infrastructure equipment connected to the core network through another of the infrastructure equipment moves away from this infrastructure equipment, or otherwise requires a different connection to the core network.

SUMMARY OF THE DISCLOSURE

The present disclosure can help address or mitigate at least some of the issues discussed above as defined in the appended claims.

Embodiments of the present technique can provide a method of communicating by a controlling communications node in a wireless backhaul network in a wireless communications network. The controlling communications node transmits a measurement configuration message to one or more other communications nodes in the wireless backhaul network formed by a plurality of communications nodes comprising the controlling communications node and at least the one or more other communications nodes, the measurement configuration message identifying one or more measurement reporting trigger conditions for each of the one or more other communications nodes which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected. The wireless backhaul network is configured to communicate data from a core network of the wireless communications network for transmitting to one or more communications devices or to communicate data to the core network received from the one or more communications devices. At least one of the plurality of communications nodes is a donor communications node having a physical connection to the core network and providing communications resources for the plurality of communications nodes to form the wireless backhaul network. The controlling communications node configures a reconfiguration message in response to receiving measurements from one or more other communications nodes from which measurements were received including one or more handover trigger conditions set by the controlling communications node to control a handover of the one or more communications nodes from which measurements were received to one or more others of the plurality of communications nodes from which radio signals can be detected in which the handover results in a change of network topology of the wireless backhaul network to communicate the data received from the core network to the one or more communications devices or to communicate the data received from the one or more communications devices to the core network. The controlling communications node arranges for the reconfiguration message to be transmitted to the one or more other communications nodes from which measurements were received. For example the controlling communications node can transmit the reconfiguration message to a source communications node to which a migrating node is attached, the source communications node then transmitting the reconfiguration message to the migrating node.

According to example embodiments, the controlling communications node can control proactively a change of network topology of the wireless backhaul network in accordance with radio conditions experienced by the nodes of the backhaul network by controlling the measurement reporting trigger conditions and the one or more handover trigger conditions.

Other embodiments of the present technique can provide a method of communicating by a communications node in a wireless backhaul network in a wireless communications network. The communications node receives from a controlling communications node a measurement configuration message. The wireless backhaul network is formed by a plurality of communications nodes comprising the communications node which received the measurement configuration message and the controlling node, the measurement configuration message identifying measurement reporting trigger conditions for the communications node which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected. The wireless backhaul network is configured to communicate data from a core network of the wireless communications network for transmitting to one or more communications devices or to communicate data to the core network received from the one or more communications devices. At least one of the plurality of communications node is a donor communications node and has a physical connection to the core network and providing communications resources for the plurality of communications nodes to form the wireless backhaul network. The communications node receives a reconfiguration message including one or more handover trigger conditions set by the controlling communications node to control a handover of the communications node which received the measurement configuration to one or more others of the plurality of communications nodes from which radio signals can be detected in which the handover results in a change of network topology of the wireless backhaul network to communicate the data received from the core network to the one or more communications devices or to communicate the data received from the one or more communications devices to the core network.

Other embodiments of the present technique can provide a method of communicating by a donor communications node in a wireless backhaul network in a wireless communications network. The donor communications node receives from a communications node, a route status check request requesting the donor communications node to check a status of one or more routes in the wireless backhaul network for communicating data between one or more communications devices and a core network of the wireless communications network, the wireless backhaul network comprising the communications node, a first set of communications nodes and the donor communications node. The donor communications node has a physical connection to the core network and provides radio resources to the communications node and the first set of communications nodes. At least one of the routes comprises a radio communications link between the communications node and a first intermediate communications node of the first set upstream of the communications node and a radio communications link between the donor communications node and either the first intermediate communications node or a second intermediate communications node of the first set upstream from the communications node. The donor communications node checks the status of the one or more routes requested in the route status check request. The donor communications node uses the status of the one or more routes to determine whether the communications node should handover to one of the first set of communications nodes other than the first intermediate communications node or to arrange a handover of one of the first set of communications nodes to another of the first set of communications nodes in which the handover results in a change of network topology of the wireless backhaul network to communicate the data between the one or more communications devices and the core network.

Other embodiments of the present technique can provide a method of communicating by a communications node in a wireless backhaul network in a wireless communications network. The communications node determines, based on one or more pre-defined conditions, whether a status of one or more routes in the wireless backhaul network for communicating data between one or more communications devices and a core network of the wireless communications network should be checked. The wireless backhaul network comprising the communications node, a first set of communications nodes and a donor communications node having a physical connection to the core network and providing radio resources to the communications node and the first set of communications nodes. At least one of the routes comprises a radio communications link between the communications node and a first intermediate communications node of the first set upstream of the communications node and a radio communications link between the donor communications node and either the first intermediate communications node or a second intermediate communications node of the first set upstream from the communications node. The communications node transmits, to the donor communications node, a route status check request requesting the donor communications node to check the status of the one or more routes. The status of the one or more routes is used by the donor communications node to determine whether the communications node should handover to one of the first set of communications nodes other than the first intermediate communications node or to arrange a handover of one of the first set of communications nodes to another of the first set of communications nodes in which the handover results in a change of network topology of the wireless backhaul network to communicate the data between the one or more communications devices and the core network.

Respective aspects and features of the present disclosure are defined in the appended claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the present technology. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein like reference numerals designate identical or corresponding parts throughout the several views, and wherein:

Figure 1 schematically represents some aspects of a LTE-type wireless telecommunication system which may be configured to operate in accordance with certain embodiments of the present disclosure;

Figure 2 schematically represents some aspects of a new radio access technology (RAT) wireless communications system which may be configured to operate in accordance with certain embodiments of the present disclosure;

Figure 3 is a schematic block diagram of some components of the wireless communications system shown in Figure 2 in more detail in order to illustrate example embodiments of the present technique; Figure 4 schematically represents some aspects of an example wireless telecommunication network which may be configured to operate in accordance with certain embodiments of the present disclosure;

Figure 5 is reproduced from [3], and provides a first example of an Integrated Access and Backhaul (IAB) deployment scenario;

Figure 6 A is reproduced from [5], and provides a second example of an IAB deployment scenario in which there are multiple candidate routes each comprising multiple hops from the end node to the donor node;

Figure 6B is an extended version of Figure 6A, providing a third example of an IAB deployment scenario in which there are multiple candidate routes each comprising multiple hops from the end node to the donor node;

Figure 7 is a block diagram illustrating a first possible network architecture for providing a wireless backhaul by means of IAB in a wireless telecommunication network which may be configured to operate in accordance with certain embodiments of the present disclosure;

Figure 8 illustrates an example of a processing procedure for a conventional handover;

Figure 9 is a schematic diagram illustrating an example of intra-donor migration in accordance with some embodiments of the present disclosure;

Figure 10 is a schematic diagram illustrating an example of inter-donor migration in accordance with some embodiments of the present disclosure;

Figure 11 illustrates an example of a processing procedure according to some embodiments;

Figure 12 illustrates an example of a processing procedure according to some embodiments;

Figure 13 illustrates a method of communicating in a wireless communications network according to some embodiments; Figure 14 illustrates a method of communicating in a wireless communications network according to some embodiments;

Figure 15 illustrates a method of communicating in a wireless communications network according to some embodiments; and

Figure 16 illustrates a method of communicating in a wireless communications network according to some embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS Long Term Evolution (LTE) Wireless Communications System

Figure 1 provides a schematic diagram illustrating some basic functionality of a mobile telecommunications network / system 6 operating generally in accordance with LTE principles, but which may also support other radio access technologies, and which may be adapted to implement embodiments of the disclosure as described herein. Various elements of Figure 1 and certain aspects of their respective modes of operation are well-known and defined in the relevant standards administered by the 3GPP (RTM) body, and also described in many books on the subject, for example, Holma H. and Toskala A [1]. It will be appreciated that operational aspects of the telecommunications networks discussed herein which are not specifically described (for example in relation to specific communication protocols and physical channels for communicating between different elements) may be implemented in accordance with any known techniques, for example according to the relevant standards and known proposed modifications and additions to the relevant standards.

The network 6 includes a plurality of base stations 1 connected to a core network 2. Each base station provides a coverage area 3 (i.e. a cell) within which data can be communicated to and from communications devices 4.

Although each base station 1 is shown in Figure 1 as a single entity, the skilled person will appreciate that some of the functions of the base station may be carried out by disparate, inter-connected elements, such as antennas (or antennae), remote radio heads, amplifiers, etc. Collectively, one or more base stations may form a radio access network.

Data is transmitted from base stations 1 to communications devices 4 within their respective coverage areas 3 via a radio downlink. Data is transmitted from communications devices 4 to the base stations 1 via a radio uplink. The core network 2 routes data to and from the communications devices 4 via the respective base stations 1 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 2 may include connectivity to the internet or to external telephony services. The core network 2 may further track the location of the communications devices 4 so that it can efficiently contact (i.e. page) the communications devices 4 for transmitting downlink data towards the communications devices 4.

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.

New Radio Access Technology (5G) Wireless Communications System

An example configuration of a wireless communications network which uses some of the terminology proposed for NR and 5G is shown in Figure 2. A 3GPP Study Item (SI) on New Radio Access Technology (NR) has been defined [2]. In Figure 2 a plurality of transmission and reception points (TRPs) 10 are connected to distributed control units (DUs) 41, 42 by a connection interface represented as a line 16. Each of the TRPs 10 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 10, forms a cell of the wireless communications network as represented by a circle 12. As such, wireless communications devices 14 which are within a radio communications range provided by the cells 12 can transmit and receive signals to and from the TRPs 10 via the wireless access interface. Each of the distributed units 41, 42 are connected to a central unit (CU) 40 (which may be referred to as a controlling node) via an interface 46. The central unit 40 is then connected to the a core network 20 which may contain all other functions required to transmit data for communicating to and from the wireless communications devices and the core network 20 may be connected to other networks 30.

The elements of the wireless access network shown in Figure 2 may operate in a similar way to corresponding elements of an LTE network as described with regard to the example of Figure 1. It will be appreciated that operational aspects of the telecommunications network represented in Figure 2, and of other networks discussed herein in accordance with embodiments of the disclosure, which are not specifically described (for example in relation to specific communication protocols and physical channels for communicating between different elements) may be implemented in accordance with any known techniques, for example according to currently used approaches for implementing such operational aspects of wireless telecommunications systems, e.g. in accordance with the relevant standards.

The TRPs 10 of Figure 2 may in part have a corresponding functionality to a base station or eNodeB of an FTE network. Similarly the communications devices 14 may have a functionality corresponding to the UE devices 4 known for operation with an FTE 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 FTE or other known mobile telecommunications standards. Flowever, 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 FTE wireless communications network.

In terms of broad top-level functionality, the core network 20 connected to the new RAT telecommunications system represented in Figure 2 may be broadly considered to correspond with the core network 2 represented in Figure 1 , and the respective central units 40 and their associated distributed units / TRPs 10 may be broadly considered to provide functionality corresponding to the base stations 1 of Figure 1. 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 14 is represented in Figure 2 within the coverage area of the first communication cell 12. This communications device 14 may thus exchange signalling with the first central unit 40 in the first communication cell 212 via one of the distributed units 10 associated with the first communication cell 12.

It will further be appreciated that Figure 2 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 Figures 1 and 2. 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 1 as shown in Figure 1 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 40 and / or a TRP 10 of the kind shown in Figure 2 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 Figure 2 is provided by Figure 3. In Figure 3, a TRP 10 as shown in Figure 2 comprises, as a simplified representation, a wireless transmitter 30, a wireless receiver 32 and a controller or controlling processor 34 which may operate to control the transmitter 30 and the wireless receiver 32 to transmit and receive radio signals to one or more UEs 14 within a cell 12 formed by the TRP 10. As shown in Figure 3, an example UE 14 is shown to include a corresponding transmitter 49, a receiver 48 and a controller 44 which is configured to control the transmitter 49 and the receiver 48 to transmit signals representing uplink data to the wireless communications network via the wireless access interface formed by the TRP 10 and to receive downlink data as signals transmitted by the transmitter 30 and received by the receiver 48 in accordance with the conventional operation.

The transmitters 30, 49 and the receivers 32, 48 (as well as other transmitters, receivers and transceivers described in relation to examples and embodiments of the present disclosure) 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 5G/NR standard. The controllers 34, 44, 48 (as well as other controllers described in relation to examples and embodiments of the present disclosure) 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 Figure 3, the TRP 10 also includes a network interface 50 which connects to the DU 42 via a physical interface 16. The network interface 50 therefore provides a communication link for data and signalling traffic from the TRP 10 via the DU 42 and the CU 40 to the core network 20. The interface 46 between the DU 42 and the CU 40 is known as the FI interface which can be a physical or a logical interface. The FI interface 46 between CU and DU may operate in accordance with specifications 3GPP TS 38.470 and 3GPP TS 38.473, and may be formed from a fibre optic or other wired high bandwidth connection. In one example the connection 16 from the TRP 10 to the DU 42 is via fibre optic. The connection between a TRP 10 and the core network 20 can be generally referred to as a backhaul, which comprises the interface 16 from the network interface 50 of the TRP 10 to the DU 42 and the FI interface 46 from the DU 42 to the CU 40.

Example arrangements of the present technique can be formed from a wireless communications network corresponding to that shown in Figures 1 or 2, as shown in Figure 4. Figure 4 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 100 comprises the core network 20 and a first, a second, a third and a fourth communications device (respectively 101, 102, 103 and 104) which may broadly correspond to the communications devices 4, 14 described above.

The wireless communications network 100 comprises a radio access network, comprising a first infrastructure equipment 110, a second infrastructure equipment 111, a third infrastructure equipment 112, and a fourth infrastructure equipment 113. Each of the infrastructure equipment provides a coverage area (i.e. a cell, not shown in Figure 4) within which data can be communicated to and from the communications devices 101 to 104. For example, the fourth infrastructure equipment 113 provides a cell in which the third and fourth communications devices 103 and 104 may obtain service. Data is transmitted from the fourth infrastructure equipment 113 to the fourth communications device 104 within its respective coverage area (not shown) via a radio downlink. Data is transmitted from the fourth communications device 104 to the fourth infrastructure equipment 113 via a radio uplink.

The infrastructure equipment 110 to 113 in Figure 4 may correspond broadly to the TRPs 10 of Figure 2 and Figure 3.

The first infrastructure equipment 110 in Figure 4 is connected to the core network 20 by means of one or a series of physical connections. The first infrastructure equipment 110 may comprise the TRP 10 (having the physical connection 16 to the DU 42) in combination with the DU 42 (having a physical connection to the CU 40 by means of the FI interface 46) and the CU 40 (being connected by means of a physical connection to the core network 20).

Flowever, there is no direct physical connection between any of the second infrastructure equipment 111, the third infrastructure equipment 112, and the fourth infrastructure equipment 113 and the core network 20. 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 20 via other infrastructure equipment (such as the first infrastructure equipment 110) which has a physical connection to the core network 20, even if the communications device is not currently served by the first infrastructure equipment 110 but is, for example, in the case of the wireless communications device 104, served by the fourth infrastructure equipment 113.

The second, third and fourth infrastructure equipment 111 to 113 in Figure 4 may each comprise a TRP, broadly similar in functionality to the TRPs 10 of Figure 2. In some arrangements of the present technique, one or more of the second to fourth infrastructure equipment 111 to 113 in Figure 4 may further comprise a DU 42, and in some arrangements of the present technique, one or more of the second to fourth infrastructure equipment 110 to 113 may comprise a DU and a CU.

In some arrangements of the present technique, the CU 40 associated with the first infrastructure equipment 110 may perform the function of a CU not only in respect of the first infrastructure equipment 110, but also in respect of one or more of the second, the third and the fourth infrastructure equipment 111 to 113.

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 Figure 4, each of the first to fourth infrastructure equipment 110 to 113 may therefore function as nodes. For example, a route for the transmission of uplink data from the fourth communications device 104 may consist of the fourth infrastructure equipment 113 (acting as the end node), the third infrastructure equipment 112 (acting as a relay node), and the first infrastructure equipment 110 (acting as the donor node). The first infrastructure 110, being connected to the core network 20, transmits the uplink data to the core network 20.

For clarity and conciseness in the following description, the first infrastructure equipment 110 is referred to below as the ‘donor node’, the second infrastructure equipment 111 is referred to below as ‘Node 1’, the third infrastructure equipment 112 is referred to below as ‘Node 2’ and the fourth infrastructure equipment 113 is referred to below as ‘Node 3’.

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 3 113, the Node 1 111 and the donor node 110, then the donor node 110 is an upstream node with respect to the Node 1 111, and the Node 3 113 is a downstream node with respect to the Node 1 111.

More than one route may be used for the transmission of the uplink/downlink data from/to a given communications device; this is referred to herein as ‘multi-connectivity’. For example, the uplink data transmitted by the wireless communications device 104 may be transmitted either via the Node 3 113 and the Node 2 112 to the donor node 110, or via the Node 3 113 and the Node 1 111 to the donor node 110.

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 4 (of Figure 1) or 14 (of Figure 2), 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 104) 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 110 and the second to fourth infrastructure equipment acting as the Nodes 1 to 3 111, 112, 113 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, Figure 4 illustrates four inter-node wireless communications links 130, 132, 134, 136.

Each of the inter- node wireless communications links 130, 132, 134, 136 may be provided by means of a respective wireless access interface. Alternatively, two or more of the inter-node wireless communications links 130, 132, 134, 136 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 130, 132, 134, 136 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 104 may communicate with the infrastructure equipment Node 3 113 using the wireless access interface which provides the inter-node wireless communications link 134 connecting the Node 3 113 and the Node 2 112.

The wireless access interface(s) providing the inter-node wireless communications links 130, 132, 134, 136 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 (“2G”), WCDMA (UMTS) and related standards such as HSPA and HSPA+ (“3G”), LTE and related standards including LTE-A (“4G”), and NR (“5G”)· 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 130, 132, 134, 136 may share communications resources. This may be because two or more of the inter- node wireless communications links 130, 132, 134, 136 are provided by means of a single wireless access interface or because two or more of the inter-node wireless communications links 130, 132, 134, 136 nevertheless operate simultaneously using a common range of frequencies.

The nature of the inter-node wireless communications links 130, 132, 134, 136 may depend on the architecture by which the wireless backhaul functionality is achieved.

Integrated Access and Backhaul (IAB) for NR

One area of NR under development is Integrated Access and Backhaul (IAB). Several requirements and aspects for the integrated access and wireless backhaul for NR to address are discussed in [3], which include:

- Efficient and flexible operation for both inband and outband relaying in indoor and outdoor scenarios;

- Multi-hop and redundant connectivity;

- End-to-end route selection and optimisation;

- Support of backhaul links with high spectral efficiency;

- Support of legacy NR UEs.

The stated objective of the study detailed in [3] 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.

Figure 5 shows the scenario presented in [3], where a backhaul link is provided from cell site A 501 to cells B 502 and C 504 over the air. It is assumed that cells B 502 and C 504 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 501, B 502 and C 504 have a dedicated DU unit and are controlled by the same CU.

Several architecture requirements for IAB are laid out in [4]. 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 15 NR specifications should be reused as much as possible in the design of the backhaul link, with enhancements considered.

Figure 6A is reproduced from [5], 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 601 which has a connection to the core network, two IAB nodes (a first IAB node 602 and a second IAB node 604) which have backhaul connections to the IAB donor node 601, and a third IAB node 606 (or end IAB node) which has a backhaul connection to each of the first IAB node 602 and the second IAB node 604. Each of the first IAB node 601 and third IAB node 606 has wireless access connections to UEs 608 and 610 respectively. As shown in Figure 6 A, originally the third IAB node 606 may communicate with the IAB donor node 601 via the first IAB node 602. After the second IAB node 604 emerges, there are now two candidate routes from the third IAB node 606 to the IAB donor node 601; via the first IAB node 602 and via the new second IAB node 604. The new candidate route via the second IAB node 604 will play an important role when there is a blockage in the first IAB node 602 to IAB donor node 604 links. 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.

In the case that the link between the first IAB node 602 and the third IAB node 606 is deteriorating, or the first IAB node 602 becomes overloaded, one of the nodes in the system (this could be the donor node 601 or the first IAB node 602 itself) will need to make a decision to change the route from the third IAB node 606 to the IAB donor node 601 from that via the first IAB node 602 to that via the second IAB node 604.

In Figure 6 A, only the IAB Donor gNB 601 has a fixed line backhaul into the core network. It should be assumed in this case that the traffic from all the UEs 610 within the third IAB node’s 606 coverage is backhauled firstly to the first IAB node 602. This backhaul link must compete for capacity on the component carrier serving the first IAB Node 602 with all the UEs 608 within the coverage area of the first IAB Node 602. In the relevant art, the first IAB Node 602 in such a system as that of Figure 6A is called a “hop” - it relays communications between the end (third) IAB node 606 and the donor IAB node 601. The backhaul link to the first IAB Node 602 requires enough capacity to support the traffic from all the UEs 610, bearing in mind that some of these may have stringent quality of service (QoS) requirements that translate into high traffic intensities.

Figure 6B is an extended version of Figure 6A, and shows what happens when there are multiple layers of IAB nodes in the deployment scenario. In the example of Figure 6A, the third IAB node 606 is the child node of the first IAB node 602, and the first IAB node 602 may be the parent node of the third IAB node 606. However, a parent node may not necessarily be the next node up (i.e. one hop in the uplink direction) towards the IAB donor node 601. A parent node may be more than one hop away from its child node or children nodes, and is in a general sense configured to allocate uplink communications resources to the child node. For example, the donor IAB node 601 may in fact be the parent node of the third IAB node 606. This is shown with greater clarity in Figure 6B.

In Figure 6B, in addition to IAB node 601, 602, 604 and 606 as shown in Figure 6A, there are additional IAB nodes 612 and 614 at the same layer or level of the network as IAB node 606. Below these are IAB nodes 616, 618, 620 and 622, which are now end nodes, in that they have no downlink backhaul connections to other IAB nodes. Here, it could be that the first IAB node 602 is still the parent of the third IAB node 606, but may also be the parent of IAB node 612. Further, the first IAB node 602 may be the parent of IAB nodes 616, 618 and 620 too, or may be a grandparent node to these nodes if nodes 606 and 612 are their parents. Furthermore, some child nodes may have multiple parent nodes, and can select from between them when transmitted uplink data in dependence on certain criteria, such as relative link qualities between the child node and its multiple parent nodes, or a relative load status between the parent nodes, for example.

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 [6] are described below.

Figure 7 illustrates one possible architecture, sometimes referred to as “Architecture la”, by which the donor Node 110, the Node 1 111 and the Node 3 113 may provide a wireless backhaul to provide connectivity for the UEs 104, 101, 14.

In Figure 7, each of the infrastructure equipment acting as an IAB node 111, 113 and the donor node 110, includes a distributed unit (DU) 711, 731, 42 which communicates with the UEs 14, 101, 104 and (in the case of the DUs 42, 711 associated with the donor node 110 and the Node 1 111) with the respective downstream IAB nodes 111, 113. Each of the IAB nodes 111, 113 (not including the donor node 110) includes a mobile terminal (MT) 712, 732, 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 130, 136 may be in the form of new radio (NR) “Uu” wireless interface. The mobile terminals 712, 732 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 130 which is used by the Node 1 111 for communication with the donor node 110 may also be used by the UE 14 to transmit and receive data to and from the donor node 110.

Similarly, an end node (such as the Node 3 113) may provide a Uu wireless interface 722 for the fourth UE 104 to communicate with the DU 731 of the Node 3 113.

Enhancements to IAB for New Radio (NR)

According to example IAB networks described above, an IAB network can be established between communications nodes which include a donor communications node which is connected to a core network. There are various enhancements to IAB networks which can be considered. One of those enhancements is a change in the topology as a result of a communications node migrating from one position within the network to another position within the network. Example embodiments described below relate to the situation in which a communications node migrates from one position in a backhaul network to another position in the backhaul network. As such a technical challenge is to provide techniques to reduce service interruption time caused by IAB-node migration and backhaul radio link failure (RLF) recovery to improve network performance and allow network deployments to undergo more frequent topology changes as well as to provide stable backhaul performance.

Topology adaptations in IAB networks may be triggered by integration of a new IAB node into an IAB network, detection of backhaul congestion or deterioration of backhaul link quality (for example, detection of RLF in a backhaul link).

Topology adaptation is typically triggered by transmission of a measurement report.

As will be appreciated from the above explanation, IAB nodes may be formed by communications devices such as UEs acting as IAB nodes to relay data upstream and downstream within an IAB network topology. An IAB node may also be formed from infrastructure equipment which is not physically connected to the core network. Such an infrastructure equipment may also be mobile and although providing a backhaul both upstream and downstream using a wireless access interface and either as a result of mobility or a variation in radio communications conditions can result in a change in link quality between IAB nodes. Accordingly there will be a requirement to monitor a state of radio links between IAB nodes and as this changes perform handovers to change the network topology so that an IAB node may be changed to connect to a different IAB node. According to a network topology adaptation, general principles of handover can be applied to IAB nodes in order to maintain an optimum configuration of nodes and the network topology.

One example of conditional handover principles explained in TS36.331 provides different conditions for communicating measurements to other infrastructure equipment. As will be appreciated UEs typically are arranged to perform measurements of signals received from different infrastructure equipment in order to determine whether a handover from its current (source) infrastructure equipment to a target infrastructure equipment. According to this arrangement, measurements are reported when these measurements satisfy certain conditions. Example embodiments can utilise these handover principles, which are adapted for IAB nodes. As with a conventional UE, according to example embodiments, an IAB node may make measurements continuously of received signal strength and in accordance with certain events transmit those measurements to a controlling the IAB node. In the present example the controlling IAB node is a CU according to the architects are show in Figures 7, 8 and 9.

An example of a conventional conditional handover of a UE between a source node and a target node is shown in Figure 8. The UE 902 is may be an example of a communications device. The source node 904 may be infrastructure equipment providing service to the UE 902. In some examples, the source node may be formed of a TRP, DU and CU. In other examples the source node 904 may be a gNB or eNB or any other infrastructure equipment described herein. In some examples, the source node 904 may be a relay UE. The target node 906 may similarly be any infrastructure equipment described herein or a relay UE. In step 908, a measurement configuration including one or more events is transmitted to the UE 902. The measurement configuration includes one or more events which outline conditions to be met in order to trigger transmission of a measurement report. Typically, in a conditional handover, events A3 and A5 (explained below) are included in the measurement configuration. Both events A3 and A5 involve a comparison between signal quality in a cell served by the source node and a cell served by the target node. If the UE 902 determines that the conditions outlined in events A3 and A5 are met, then it transmits a measurement report to the source node 904 in step 910. The measurement may include measurements made by the UE on one or more objects specified by the source node. The source node 904 may then configure one or more conditions to be met to perform the conditional handover to the target node 906..

In step 912, the source node performs a context update with the target node 906. In step 914, the source node 904 transmits an RRC reconfiguration message to the UE 902. The RRC reconfiguration message includes the one or more conditions configured by the source node 904 to perform the conditional handover. The UE 902 then determines, on a basis of the one or more conditions included in the RRC reconfiguration message, whether the conditions have been met. In an example, the one or more conditions included in the RRC reconfiguration message may include a minimum link quality threshold between the UE 902 and the source node 904. If the UE determines that the link quality threshold is below the minimum threshold then the UE 902 determines that the conditions outlined in the RRC reconfiguration message have been met. If the UE 902 determines that one or more conditions included in the RRC reconfiguration message have been met then, in step 916, the UE 902 establishes radio communications link with the target node 906 through a random access channel (RACH) procedure. This may be a two-step RACH or four-step RACH. In this example, the triggering of the transmission of the measurement report in step 910 (and consequently the transmission of the one or more conditions for the handover in step 914) rely on the conditions outlined in events A3 and/or A5 being met. According to one example, a central unit (such as CU 40 ) transmits a measurement configuration message including one or more events (such as events A3 and A5 (see below)) to a downstream IAB. If conditions outlined in the one or more events are met, a measurement report is transmitted from the downstream IAB node to an upstream IAB node. The measurement report is then forwarded to the CU by the upstream IAB node. The CU then transmits an RRC reconfiguration message including one or more conditions to be met to perform a handover of the downstream IAB node to a target node. If the downstream node determines that the one or more conditions included in the RRC reconfiguration message are met, then the handover is performed.

TS 36.331 outlines that the downstream IAB node will only transmit the measurement report in a case where conditions outlined in event A3 and/or event A5 are met:

Event A3: Neighbour becomes an amount of offset better than PCell/PSCell. In other words, a signal quality of a primary/secondary component carrier for a neighbouring cell becomes amount of offset better than a primary/secondary component carrier for a currently serving cell.

Event A5: PCell/PSCell becomes worse than absolute thresholdl AND Neighbour becomes better than another absolute threshold2. In other words, a signal quality of a primary/secondary component carrier for a currently serving cell becomes worse than a first absolute threshold AND a signal quality primary/secondary component carrier for a neighbouring cell becomes better than a second absolute threshold.

For example, the condition in event A3 is met if the IAB node performing the measurements determines that values obtained from measurements of one or more component carriers of a neighbouring cell are a pre-determined amount better than one or more component carriers of a serving cell of the IAB node. For example, the measurements of the one or more component carriers may include one or more of a reference signal strength indicator (RSSI), reference signal received power (RSRP) and/or a reference signal received quality (RSRQ). The condition outlined in event A3 is regarded as being met in this case if one or more of the RSSI, RSRP or RSRQ of one or more component carriers of the neighbouring cell are a pre-determined amount higher than one or more component carriers of the serving cell.

For example, the condition in event A5 is met if the IAB node performing the measurements determines that values obtained from measurements of one or more component carriers of a serving cell of the IAB node is worse than a first threshold and the values obtained from measurements of a one or more component carriers of a neighbouring cell are better than a second threshold.

In other words, the transmission of the measurement report only occurs in response to a backhaul link between the downstream IAB node and the upstream IAB node failing/becoming inferior to a neighbouring cell. The events triggering the transmission of the measurement report are therefore undesirably limited.

In other examples, if the downstream IAB node detects RLF for the backhaul link between it and the upstream IAB node, then the downstream IAB node may transmit an RLF notification to one or more other IAB nodes downstream of the downstream IAB node. The RLF notification is only transmitted when RLF has been detected. Therefore, topology adaptation in response to the RLF notification in this example relies on RLF being detected. In order to provide for increased IAB node mobility, there arises a need for proactive topology adaptation to reduce interruption time and/or guarantee service quality. In other words, there is a need for an increased flexibility in triggering topology adaptation. For example, there may arise a need to find candidate routes before an on-going route is interrupted. In this case, service interruption will be increased if network must wait for the conditions outlined in events A3 and/or A5 to be met.

Example embodiments can provide methods of triggering topology adaptation in a proactive (rather than reactive) way.

In order to further reduce service interruption time and allow an IAB network to perform more frequent topology adaption, embodiments can provide additional configurations including measurement reporting as well as handover triggers. By carefully designing conditions (triggers) to be included in the RRC reconfiguration message from the CU to the downstream IAB node, more frequent topology updates can be achieved in order to maintain a more robust backhaul link.

Intra-Donor Migration and Inter-Donor Migration

Embodiments of the present technique are applicable to both handover procedures involving intra-donor migration and handover procedures involving inter-node migration. Intra-donor migration and intra-donor migration are explained with reference to Figures 9 and 10 below.

In accordance with some embodiments, Figure 9 illustrates an example of intra-donor IAB node migration. Figure 9 illustrates a first IAB donor node 1004, a second IAB donor node 1016, a first IAB relay node 1006, a second IAB relay node 1014, a third IAB relay node 1018, a fourth IAB relay node 1020, an end node 1010, and a core network 1002. It will be appreciated that one or more of the IAB nodes in Figure 9 may provide service to one or more UEs, although no UEs are shown in Figure 9 for clarity.

The first 1004 and second 1016 IAB donor nodes are each connected to the core network 1002 by physical connections. As illustrated in Figure 9, the first IAB donor node 1004 is connected to the first IAB relay node 1006 and the second IAB relay node 1014 via backhaul links 1005, 1007. Similarly, the second IAB donor node 1016 is connected to the third IAB relay node 1018 and the fourth IAB relay node via backhaul links 1017, 1019.

As explained above, an example of intra-IAB node migration is where an IAB node in an IAB network migrates from an attachment point which connects to the core network via one IAB donor node to attach at a different point which routes data to and from the core network via the same IAB donor node.

As an example illustrated in Figure 9, initially, the end IAB node 1010 is connected to the second IAB relay node 1014 via a backhaul link 1012. In an example of intra-donor migration, the backhaul link 1012 may fail and the end IAB node 1010 may form a new connection with the first IAB relay node 1006 via a backhaul link 1008. It will be appreciated that intra donor- migration is any migration of an IAB node such that the route from the IAB node back to the core network is via the same donor IAB node. In an alternative example of intra-donor migration (not shown), the connection between the first IAB relay node 1006 and the first IAB donor node 1004 may fail and the first relay IAB 1006 node may form a new connection (via a backhaul link) with the second IAB relay node 1014.

In contrast Figure 10 illustrates an example of inter-donor IAB node migration in accordance with some embodiments. As explained above, inter-IAB node migration is where an IAB node in an IAB network migrates from an attachment point which connects to the core network via one IAB donor node to attach at a different point which routes data to and from the core network via the different IAB donor node. Figure 10 is largely based on Figure 9 and the same reference numerals will be used for corresponding features. Initially, the end IAB node 1010 is connected to the second IAB relay node 1014 via a backhaul link 1022. In an example of inter-donor migration, the backhaul link 1022 may fail and the end IAB node 1010 may form a new connection with the third IAB relay node 1018 via a backhaul link 1024.

In the examples shown in Figures 9 and 10, the end IAB node 1010 is an example of a “migrating node”.

It will be appreciated that inter donor migration is any migration of an IAB node such that the route from the IAB node back to the core network is via a different donor IAB node. In an alternative example of inter-donor migration (not shown in the Figures), the connection between the second IAB relay node 1014 and the first IAB donor node 1004 may fail. In this example, the second relay node 1014 may act as a migrating node and form a connection (via a backhaul link) with the third IAB relay node 1018, the second IAB donor node 1016 or the fourth IAB relay node 1020.

Conditional Handover for IAB in NR

In accordance with some embodiments, a measurement configuration message is transmitted from a CU of a donor IAB node to an IAB node outlining conditions for triggering transmission of a measurement report according to example embodiments. In some embodiments, an event A4 may be introduced into the RRC reconfiguration message either instead of, or in addition to, events A3 and A5 explained above. TS 36.331 defines event A4 is defined as follows:

Event A4: Neighbour becomes better than absolute threshold. In other words, a signal quality of a primary/secondary component carrier for a neighbouring cell becomes better than an absolute threshold.

For example, the condition in event A4 is met if the IAB node performing the measurements determines that values obtained from measurements (such as RSSI, RSRP and/or RSRQ) of one or more component carriers of a neighbouring cell are a better (higher in the case of RSSI, RSRP and RSRQ) than an absolute threshold.

The introduction of A4 in the measurement configuration message may be especially useful for services with a particularly high quality of service (QoS) requirement or in cases where an IAB node is mobile. In these cases, it is not desirable to rely on the measurement report transmission to be triggered by event A3 or A5.

It may be desirable for a migrating IAB node to handover from a source IAB node to a target IAB node even in a case where a backhaul link between the migrating IAB node and the source IAB node is of high quality. As explained above, the addition of event A4 in the measurement configuration message may trigger transmission of a measurement report (which may lead to handover) even in the case where the backhaul link between the migrating IAB node and the source IAB node is of high quality. Therefore an increased flexibility in topology adaptation is provided. For example, if a network desires that a new route is added in the network due to a route redundancy purpose, load balancing between routes or faster switching of traffic during handover, then event A4 may be included in a measurement configuration message(s) in order to trigger handover(s) which create the new route.

In some embodiments, a carefully designed threshold for event A4 may reduce unnecessary topology adaptation. In some embodiments, event A4 is introduced as a conditional handover trigger for IAB nodes and/or for certain services with a stringent QoS requirement. Therefore in such embodiments the trigger conditions for measurement reporting are themselves conditional on a QoS requirement of a bearer type or service being reported.

In accordance with some embodiments, Figure 11 illustrates a processing procedure for a conditional handover (intra-donor migration or intra-donor migration) in a case in which event A4 is included as a measurement report trigger. As explained above, event A4 may be included as a measurement report trigger if data being transmitted has a high QoS requirement or an IAB node receiving the data has a high mobility, for example. The handover process illustrated in Figure 10 involves radio communication between a migrating IAB node (such as migrating node 1010), a source IAB node (such as the second relay node 1014), a target IAB node 1204 (such as the first relay node 1006 in Figure 9 or the third relay node 1024 in Figure 10). A Central Unit (CU) 1202 is also provided in Figure and may be assumed to be physically connected to the core network 1002. The CU 1202 may form part of a donor IAB node such as the first donor node 1004. The communications shown in Figure 10 may be performed between a Mobile Terminal (MT) of the migrating IAB node 1010 (hereinafter referred to as the “migrating node 1010”), a DU of the source IAB node 1014 (hereinafter referred to as the “source node 1014”) and a DU of the target IAB node 604 (hereinafter referred to as the “target node 604”).

It will be appreciated that an IAB node may be a network node having IAB-MT functionality. The IAB- MT functionality may be substantially the same as UE functionality . The IAB node may be a relay base station or a UE for example. The IAB node may be deployed by the network or may appear in the network in an un-coordinated manner.

The migrating node 1010 may perform radio communication with the source node 1014 via a backhaul link (as was shown in Figures 9 and 10). In step 1204, the CU 1202 transmits a measurement configuration to the migrating node 1010. The measurement configuration may be included in an RRC reconfiguration message. The measurement configuration may include one or more of the following parameters:

- Measurement objects: Objects on which the migrating node 1010 is to perform measurements. In other words, an indication of what the migrating node 1010 is to measure.

- Reporting criteria/Measurement Report Triggers: Criteria that trigger the migrating node 1010 to send a measurement report. This can either be periodical or a single event description.

- Reporting format: Quantities that the migrating node 1010 includes in the measurement report and associated information (for example a number of cells to report).

- Measurement identities: Each measurement identity links one measurement object with one reporting configuration. By configuring multiple measurement identities it is possible to link more than one measurement object to the same reporting configuration, as well as to link more than one reporting configuration to the same measurement object.

- Quantity configurations: A quantity configuration defines the measurement quantities and associated filtering used for all event evaluation and related reporting of that measurement type. - Measurement gaps: Periods that the migrating node 1010 may use to perform measurements (for example when no UL and DL transmissions are scheduled.

As part of the reporting criteria/measurement report triggers, some embodiments include events A3, A4 and/or event A5. In other words, if the conditions outlined in events A3, A4 and/or A5 are met based on measurements carried out by the migrating node 1010, then the migrating node 1010 may transmit a measurement report. Step 1206 illustrates the transmission of the measurement report from the migrating node 1010 to the source node 1014 based on, for example, the condition outlined in event A4 being met. The migrating node 1010 may determine that the condition in event A4 is met because it determines that a cell of a neighbouring IAB (such as the target node 604) is better than an absolute threshold. For example, the migrating node 1010 determines that a value of RSSI, RSRP and/or RSRQ of the cell of the target node 604 is higher than an absolute threshold. In step 1208, the source node 1014 forwards the measurement report onto the CU 1202. In response to receiving the measurement report, the CU 1202 performs a UE context update procedure with the target node 604 in step 1210.The UE context update procedure may include context set-up with an MT of the target IAB node 1204. For example, the context set-up may involve radio link control (RLC) channel establishment and/or a set up of one or more IAB- MT bearers with the target node 1204.

In step 1212, the CU 1202 transmits an RRC reconfiguration message to the source node 1014 . In step 1214, the source node 1014 forwards the RRC reconfiguration to the migrating node 1010. The RRC reconfiguration message includes one or more conditions to be met for the handover of the migrating node 1010 from the source node 1014 to the target node 1204. The migrating node 1010 then determines if the one or more conditions outlined in the RRC reconfiguration message are met. The one or more conditions may be different from the conditions outlined in events A3, A4 or A5. In an example, the one or more conditions may be that a link quality of the radio link between the migrating node 1010 and the source node 1014 falls below a pre-determined threshold. In this example, the migrating node 1010 may determine that the one or more conditions are met if the quality of the radio link between the migrating node 1010 and the source node 1014 falls below the pre-determined threshold in the RRC reconfiguration message. In step 1216, if the migrating node 1010 determines that the one or more conditions outlined in the RRC reconfiguration message have been met, then the migrating node 1010 performs a Random Access Channel (RACH) procedure (such as a 2-step RACH or a 4-step RACH) with the target node 1204 to establish a backhaul link between the migrating node 1010 and the target node 1204. In step 1218, a path switch operation occurs between the source node 1014 and the CU 1202. In some embodiments, the path switch operation may involve releasing a current path between an MT of the migrating node and a DU of the source node. In step 1220, the source node releases radio resources which it reserved for the migrating node 1010.

In some embodiments, such as the embodiment shown in Figure 11, the measurement configuration is signalled from the CU 1202 to the migrating node 1010 by RRC signalling in step 1204. In other embodiments the measurement configuration may be transmitted from the CU 1202 to the source node 1014 (in particular to the DU of the source node 1014) via FI Application Protocol (F1AP). Then the source node 1204 configures the migrating node 1010 with the measurement configuration via RRC signalling.

As will be appreciated another of the IAB nodes in a network topology other than the CU or donor IAB node may control the architecture and the topology, so that the trigger conditions and reporting and handover direction may be performed by a node other than the donor node. As will be appreciated by a person skilled in the art, the inclusion of event A4 as a measurement report trigger prompts the CU 1202 to configure the migrating node 1010 with one or more conditions for the conditional handover provided the conditions outlined in event A4 are met. In other words, event A4 also triggers the transmission of the RRC reconfiguration message in step 1212. Since event A4 only requires a signal quality of one or more component carriers for a neighbouring cell to be better than an absolute threshold, embodiments provide an increased flexibility in topology adaption in an IAB network,

Route Status Check Request

A downstream IAB node can only monitor a backhaul link between itself and an upstream IAB node. Therefore, the downstream IAB node cannot obtain current link status information about each hop of a route between the downstream IAB node and the core network. This lack of flexibility may create a number of service continuity problems. For example, with reference to Figure 9, the migrating node 1010 is initially connected to the second relay node 1014 via a first backhaul link 1012 and the second relay node is connected to the first donor node 1004 via a second backhaul link 1007. In a case where data is transmitted successfully from the migrating node 1010 to the second relay node 1014 via the first backhaul link 1012 but cannot be transmitted successfully from the second relay node 1014 to the core network (for example, because of a problem with the second backhaul link 1007 between the second relay node 1014 and the first donor node 1004), the migrating node 1010 will be unaware of this failure.

The second relay node 1014 may avoid the failure by handing over to another node but must rely on the conditions in events A3 and A5 being met (as discussed above). This is not always desirable because it may introduce further delay.

In accordance with some embodiments, a downstream IAB node sends a route status check request to a CU via an upstream IAB node. The CU then checks routes from the downstream IAB node to a core network and decides to perform handover if it detects backhaul link performance degradation in backhaul links along the routes

Figure 12 is largely based on Figure 11 and the same reference numerals will be used for corresponding entities. In step 1302, the migrating node 1010 sends a route status check request to the source node 1014.

The transmission of the route status request may be triggered if the migrating node 1010 detects one or more of the following:

- Detection of reception of data which exceeds a buffer capacity of the migrating node 1010

- Detection of one or more routes in a route table maintained at the migrating node 1010 having a common next-hop IAB node. The routing table may have been configured for the migrating node by a CU.

- Detection of received data with a stringent QoS requirement

- Detection of a change in the mobility of the migrating node (for example, from high mobility to low mobility)

- Detection of poor performance on one or more routes from the migrating node to one or more destination nodes, even if there is no problem detected with a next-hop node. For example, the migrating node may determine that application layer data transmission on the one or more routes is delayed even though no problem has been detected with the radio link between the migrating node 1010 and the next hop node. The route status check request transmitted in step 1302 may contain an indication of one or more of the following:

- Routes to be checked: For example, the route status check request may indicate to the CU 1202 that all routes with a common next hop IAB node should be checked. In other examples, the route status check request may indicate to the CU to check information regarding specific IAB nodes.

- Reason to send the request: For example, the route status check request may include an indication of the trigger which caused the transmission of the route status check request in step 1302. This gives the CU 1202 additional information on how urgent the request is. For example, a route status check request triggered by an influx of data to the migrating node 1010 with a stringent QoS requirement may indicate that to the CU 1202 that a route status check is more urgent than if the route status check request was triggered by the migrating node 1010 detecting that its mobility changes from low to high.

- Measurement report: The measurement report may correspond to the measurement report in Figure 11. This measurement report may provide the CU 1202 an up-to-date link status of the migrating node with its neighbour nodes.

It will be appreciated that references to “routes” may mean any route for data transmission in the wireless communication network. For example, “routes” may mean routes for data transmission between a node and a core network. In this example, a route may be comprised of one or more hops (other IAB nodes or infrastructure equipment or UEs or the like) between the IAB node and the core network connected by radio communications links. In this example, data transmitted by the IAB node is transmitted in turn to the one or more hops and eventually to the core network. The IAB node may have multiple routes to the core network. In some examples, one or more routes from the IAB node to the core network may have one or more common hops. In some examples, in a distributed scheme, the IAB maintains possible routes for data transmission to the core network in a routing table.

In step 1304, the source node 1014 forwards the route status check request onto the CU 1202. Although, the CU 1202 receives the route status check request, it is not required to respond to the migrating node 1010 with route status information. In response to receiving the route status check request, the CU 1202 will check a link status between hops. In some embodiments, the CU 1202 may check a link status between hops indicated in the measurement report .In other embodiments the CU may check a link status between hops indicated in a report from a DU of the source node. If the CU 1202 detects link performance degradation between one or more backhaul links then the CU 1202 may perform one or more of the following:

- Instruct the migrating node 1010 to handover to the target node 1204 in order to avoid IAB nodes which have a backhaul link with degraded performance.

- Update routing tables on IAB nodes on routes which have an IAB node with a backhaul link with degraded performance.

- Adjust configurations of measurement, reporting criteria and/or handover conditions of particular IAB nodes in order to encourage handover.

In response to receiving the route status check request, the CU 1202 performs a UE context update procedure with the target node 1204 in step 1306. In step 1308, the CU 1202 transmits an RRC reconfiguration message to the source node 1014. In step 1310, the source node 1014 transmits an RRC reconfiguration to the migrating node 1010. In step 1312, the migrating node 1010 performs a Random Access Channel (RACH) procedure (such as a 2-step RACH or a 4-step RACH) with the target node 1204 to establish a backhaul link between the migrating node 1010 and the target node 1204 (such as backhaul link 1008 or 1024). In step 1314, a path switch operation occurs between the source node 1014 and the CU 1202. In step 1316, the source node releases radio resources which it reserved for the migrating node 1010.

In some embodiments, such as the embodiment shown in Figure 12, the route status check request is signalled from an MT of the migrating node 1010 to the CU 1202 by RRC signalling in step 1304. In other embodiments, the route status check request may be transmitted from a DU of the migrating node 1010 to the CU 1202 via FI Application Protocol (F1AP).

As will be appreciated by a person skilled in the art, the proactive step of transmitting the route status check request enables the CU 1202 to determine if problems for data transmission are likely to be encountered on one or more routes to a core network. The CU 1202 may then perform topology adaptation in response to this determination. In other words, the CU 1202 is not required to wait until it receives RLF notifications before it performs topology adaptation. Embodiments therefore provide an increased flexibility in topology adaptation in an IAB network.

Figure 13 illustrates a method of communicating by a controlling communications node in a wireless backhaul network in a wireless communications network. The method starts at step 1500. In step 1502, the controlling communications node transmits a measurement configuration message to one or more other communications nodes in the wireless backhaul network formed by a plurality of communications nodes comprising the controlling communications node and at least the one or more other communications nodes, the measurement configuration message identifying measurement reporting trigger conditions for each of the one or more other communications nodes which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected. The wireless backhaul network is configured to communicate data from a core network of the wireless communications network for transmitting to one or more communications devices or to communicate data to the core network received from the one or more communications devices. At least one of the plurality of communications nodes is a donor communications node having a physical connection to the core network and providing communications resources for the plurality of communications nodes to form the wireless backhaul network. In step 1504, the controlling communications node configures a reconfiguration message in response to receiving measurements from one or more other communications nodes which received the measurement configuration message including one or more handover trigger conditions set by the controlling communications node to control a handover of the one or more communications nodes from which measurements were received to one or more others of the plurality of communications nodes from which radio signals can be detected in which the handover results in a change of network topology of the wireless backhaul network to communicate the data received from the core network to the one or more communications devices or to communicate the data received from the one or more communications devices to the core network. In step 1506, the controlling communications node arranges for the reconfiguration message to be transmitted to the one or more other communications nodes which received the measurement configuration message. In some embodiments, the controlling node transmits the measurement configuration message. In other nodes, the controlling node transmits the reconfiguration message to a source node for forwarding on as in the example shown in Figure 12.The method ends at step 1508. In some embodiments, the controlling communications node may be a central unit (CU) which is connected to the core network. In other embodiments, the controlling node may be formed of the central unit and a distributed unit (DU). In some embodiments, the DU may be an intermediate source node between the CU and the one or others of the plurality of communications nodes. In this embodiment, transmissions and receptions from or to the controlling node may via the source node.

Figure 14 a method of communicating by a communications node in a wireless backhaul network in a wireless communications network. The method starts at step 1600. In step 1602, the communications node receives from a controlling communications node a measurement configuration message. The wireless backhaul network is formed by a plurality of communications nodes comprising the communications node which received the measurement configuration message and the controlling node, the measurement configuration message identifying measurement reporting trigger conditions for the communications node which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected. The wireless backhaul network is configured to communicate data from a core network of the wireless communications network for transmitting to one or more communications devices or to communicate data to the core network received from the one or more communications devices. At least one of the plurality of communications node being a donor communications node having a physical connection to the core network and providing communications resources for the plurality of communications nodes to form the wireless backhaul network. In step 1604, the communications node receives a reconfiguration message including one or more handover trigger conditions set by the controlling communications node to control a handover of the communications node which received the measurement configuration to the one or more others of the plurality of communications nodes from which radio signals can be detected in which the handover results in a change of network topology of the wireless backhaul network to communicate the data received from the core network to the one or more communications devices or to communicate the data received from the one or more communications devices to the core network. The method ends at step 1606.

Figure 15 illustrates a method of communicating by a donor communications node in a wireless backhaul network in a wireless communications network. The method starts at step 1700. In step 1702, the donor communications node receives from a communications node, a route status check request requesting the donor communications node to check a status of one or more routes in the wireless backhaul network for communicating data between one or more communications devices and a core network of the wireless communications network, the wireless backhaul network comprising the communications node, a first set of communications nodes and the donor communications node. The donor communications node has a physical connection to the core network and provides radio resources to the communications node and the first set of communications nodes. At least one of the routes comprises a radio communications link between the communications node and a first intermediate communications node of the first set upstream of the communications node and a radio communications link between the donor communications node and either the first intermediate communications node or a second intermediate communications node of the first set upstream from the communications node. In step 1704, the donor communications node checks the status of the one or more routes requested in the route status check request. In step 1706, the donor communications node uses the status of the one or more routes to determine whether the communications node should handover to one of the first set of communications nodes other than the first intermediate communications node or to arrange a handover of one of the first set of communications nodes to another of the first set of communications nodes in which the handover results in a change of network topology of the wireless backhaul network to communicate the data between the one or more communications devices and the core network. The method ends at step 1708.

Figure 16 illustrates a method of communicating by a communications node in a wireless backhaul network in a wireless communications network. The method starts at step 1800. In step 1802, the communications node determines, based on one or more pre-defined conditions, whether a status of one or more routes in the wireless backhaul network for communicating data between one or more communications devices and a core network of the wireless communications network should be checked,. The wireless backhaul network comprising the communications node, a first set of communications nodes and a donor communications node having a physical connection to the core network and providing radio resources to the communications node and the first set of communications nodes. At least one of the routes comprises a radio communications link between the communications node and a first intermediate communications node of the first set upstream of the communications node and a radio communications link between the donor communications node and either the first intermediate communications node or a second intermediate communications node of the first set upstream from the communications node. In step 1804, the communications node transmits, to the donor communications node, a route status check request requesting the donor communications node to check the status of the one or more routes. The status of the one or more routes is used by the donor communications node to determine whether the communications node should handover to one of the first set of communications nodes other than the first intermediate communications node or to arrange a handover of one of the first set of communications nodes to another of the first set of communications nodes in which the handover results in a change of network topology of the wireless backhaul network to communicate the data between the one or more communications devices and the core network. The method ends at step 1808.

The following numbered paragraphs provide further example aspects and features of the present technique:

Paragraph 1. A method of communicating by a controlling communications node in a wireless backhaul network in a wireless communications network, the method comprising transmitting from the controlling communications node a measurement configuration message to one or more other communications nodes in the wireless backhaul network formed by a plurality of communications nodes comprising the controlling communications node and at least the one or more other communications nodes, the measurement configuration message identifying measurement reporting trigger conditions for each of the one or more other communications nodes which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected, the wireless backhaul network being configured to communicate data from a core network of the wireless communications network for transmitting to one or more communications devices or to communicate data to the core network received from the one or more communications devices, at least one of the plurality of communications nodes being a donor communications node having a physical connection to the core network and providing communications resources for the plurality of communications nodes to form the wireless backhaul network; configuring, in response to receiving measurements from one or more other communications nodes which received the measurement configuration message, a reconfiguration message including one or more handover trigger conditions set by the controlling communications node to control a handover of the one or more other communications nodes from which measurement were received to one or more others of the plurality of communications nodes from which radio signals can be detected in which the handover results in a change of network topology of the wireless backhaul network to communicate the data received from the core network to the one or more communications devices or to communicate the data received from the one or more communications devices to the core network; and arranging for the reconfiguration message to be transmitted to the one or more other communications nodes from which measurements were received.

Paragraph 2. A method according to paragraph 1, wherein the measurement reporting trigger conditions for each of the one or more other communications nodes which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected comprise an absolute threshold of a measured signal parameter of one or more component carriers for the one or more others of the plurality of communications nodes from which radio signals can be detected.

Paragraph 3. A method according to paragraphs 1 or 2, wherein the measurement reporting trigger conditions for each of the one or more other communications nodes which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected comprise a difference in a measured signal parameter of one or more component carriers of the one or more others of the plurality of communications nodes from which radio signals can be detected with respect to the measured signal parameter a current communication node.

Paragraph 4. A method according to paragraphs 1, 2 or 3, wherein the measurement reporting trigger conditions for each of the one or more other communications nodes which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected comprise a first absolute threshold of a measured signal parameter of one or more component carriers for the one or more others of the plurality of communications nodes from which radio signals can be detected and a second absolute threshold of a measured signal parameter of one or more component carriers of the current communications node.

Paragraph 5. A method according to any of paragraphs 1 to 4, wherein the absolute threshold is a pre defined threshold of one or more of a received signal strength indicator (RSSI), reference signal received power (RSRP) and/or a reference signal received quality (RSRQ) of the one or more component carriers for the one or more others of the plurality of communications nodes from which radio signals can be detected.

Paragraph 6. A method according to any of paragraphs 1 to 5, comprising receiving, from a first of the one or more other communications nodes which received the measurement configuration message, a measurement report providing an indication of measurements of radio signals received from a second of the one or more others of the plurality of communications nodes from which radio signals can be detected.

Paragraph 7. A method according to any of paragraphs 1 to 6, wherein transmitting from the controlling communications node a measurement configuration message to one or more other communications nodes in the wireless backhaul network comprises transmitting the measurement configuration message from a central unit (CU) of the controlling node to a distributed unit (DU) via FI Application Protocol (F1AP) signalling; and transmitting the measurement configuration message from the DU to a Mobile Terminal (MT) of a first communications node of the one or more other communications nodes in the wireless backhaul network via RRC signalling.

Paragraph 8. A method according to any of paragraphs 1 to 7, wherein the controlling node is the donor node having the physical connection to the core network and providing the radio resources for the plurality of communications nodes in the wireless backhaul network.

Paragraph 9. A method of communicating by a communications node in a wireless backhaul network in a wireless communications network, the method comprising determining, by the communications node, based on one or more pre-defined conditions, whether a status of one or more routes in the wireless backhaul network for communicating data between one or more communications devices and a core network of the wireless communications network should be checked, the wireless backhaul network comprising the communications node, a first set of communications nodes and a donor communications node having a physical connection to the core network and providing radio resources to the communications node and the first set of communications nodes, wherein at least one of the routes comprises a radio communications link between the communications node and a first intermediate communications node of the first set upstream of the communications node and a radio communications link between the donor communications node and either the first intermediate communications node or a second intermediate communications node of the first set upstream from the communications node; transmitting, to the donor communications node, a route status check request requesting the donor communications node to check the status of the one or more routes, the status of the one or more routes being used by the donor communications node to determine whether the communications node should handover to one of the first set of communications nodes other than the first intermediate communications node or to a handover of one of the first set of communications nodes to another of the first set of communications nodes in which the handover results in a change of network topology of the wireless backhaul network to communicate the data between the one or more communications devices and the core network.

Paragraph 10. A method according to paragraph 9, comprising receiving a command from the donor communications node to handover from a first attachment point to the first intermediate communications node which is currently being used to communicate the data via the radio communications link between the communications node and the first intermediate node to a second attachment point providing a radio link between the communications node and one of the first set of communications nodes other than the first intermediate communications node.

Paragraph 11. A method according to paragraph 10, wherein the command received from the donor communications node to handover includes a configuration for the handover.

Paragraph 12. A method according to paragraphs 9 to 11, wherein the one or more pre-defined conditions include a detection, by the communications node, of one or more of: an amount of data in a buffer of the communications node exceeding a buffer capacity of the communications node, one or more routes in a routing table maintained at the communications node have a common hop or a performance degradation, data with a stringent Quality of Service (QoS) requirement being received at the communications node, a change in a mobility status of the communications node.

Paragraph 13. A method according to any of paragraphs 9 to 12, wherein the route status check request includes one or more of an indication of which routes should be checked, an indication of one or more pre-defined condition which caused the request to be transmitted, a measurement report.

Paragraph 14. A method of communicating by a communications node in a wireless backhaul network in a wireless communications network, the method comprising receiving from a controlling communications node a measurement configuration message, the wireless backhaul network being formed by a plurality of communications nodes comprising the communications node which received the measurement configuration message and the controlling node, the measurement configuration message identifying measurement reporting trigger conditions for the communications node which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected, the wireless backhaul network being configured to communicate data from a core network of the wireless communications network for transmitting to one or more communications devices or to communicate data to the core network received from the one or more communications devices, at least one of the plurality of communications nodes being a donor communications node having a physical connection to the core network and providing communications resources for the plurality of communications nodes to form the wireless backhaul network; receiving a reconfiguration message including one or more handover trigger conditions set by the controlling communications node to control a handover of the communications node which received the measurement configuration to one or more others of the plurality of communications nodes from which radio signals can be detected in which the handover results in a change of network topology of the wireless backhaul network to communicate the data received from the core network to the one or more communications devices or to communicate the data received from the one or more communications devices to the core network.

Paragraph 15. A method according to paragraph 14, wherein the measurement trigger conditions for the communications node to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected comprise an absolute threshold of a measured signal parameter of one or more component carriers for the one or more others of the plurality of communications nodes from which radio signals can be detected.

Paragraph 16. A method according to paragraphs 14 or 15, wherein the measurement reporting trigger conditions for the communications node to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected comprises a difference in a measured signal parameter of one or more component carriers of the one or more others of the plurality of communications nodes from which radio signals can be detected with respect to the measured signal parameter a current communication node.

Paragraph 17. A method according to paragraphs 14, 15 or 16, wherein the measurement reporting trigger conditions for the communications node to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected comprise a first absolute threshold of a measured signal parameter of one or more component carriers for the one or more others of the plurality of communications nodes from which radio signals can be detected and a second absolute threshold of a measured signal parameter of one or more component carriers of the current communications node.

Paragraph 18. A method according to any of paragraphs 14 to 17, wherein the absolute threshold is a pre-defined threshold of one or more of a received signal strength indicator (RSSI), reference signal received power (RSRP) and/or a reference signal received quality (RSRQ) of the one or more component carriers for the one or more others of the plurality of communications nodes from which radio signals can be detected.

Paragraph 19. A method according to any of paragraphs 14 to 18, comprising determining whether or not the measurement reporting trigger conditions for the communications node to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected included in the measurement configuration received from the controlling communications node are met, and if the trigger conditions are met, transmitting a measurement report to the controlling communications node.

Paragraph 20. A method according to any of paragraphs 12 to 19, wherein the controlling node is the donor node having the physical connection to the core network and providing the radio resources for the plurality of communications nodes in the wireless backhaul network.

Paragraph 21. A method of communicating by a donor communications node in a wireless backhaul network in a wireless communications network, the method comprising receiving, from a communications node, a route status check request requesting the donor communications node to check a status of one or more routes in the wireless backhaul network for communicating data between one or more communications devices and a core network of the wireless communications network, the wireless backhaul network comprising the communications node, a first set of communications nodes and the donor communications node, the donor communications node having a physical connection to the core network and providing radio resources to the communications node and the first set of communications nodes, wherein at least one of the routes comprises a radio communications link between the communications node and a first intermediate communications node of the first set upstream of the communications node and a radio communications link between the donor communications node and either the first intermediate communications node or a second intermediate communications node of the first set upstream from the communications node; and checking the status of the one or more routes requested in the route status check request; using the status of the one or more routes to determine whether the communications node should handover to one of the first set of communications nodes other than the first intermediate communications node or to arrange a handover of one of the first set of communications nodes to another of the first set of communications nodes in which the handover results in a change of network topology of the wireless backhaul network to communicate the data between the one or more communications devices and the core network.

Paragraph 22. A method according to paragraph 21, comprising transmitting a command to the communications node to handover from a first attachment point to the first intermediate communications node which is currently being used to communicate the data via the radio communications link between the communications node and the first intermediate node to a second attachment point providing a radio link between the communications node and one of the first set of communications nodes other than the first intermediate communications node.

Paragraph 23. A method according to paragraph 21, comprising transmitting a command to one of the first set of communications nodes to handover to another of the first set of communications nodes

Paragraph 24. A method according to any of paragraphs 21 to 23, wherein the route status check request includes one or more of an indication of which routes should be checked, an indication of one or more pre-defined conditions which caused the request to be transmitted, and a measurement report.

Paragraph 25. A method according to any of paragraphs 21 to 24, comprising determining that a performance of one or more radio communications links on the one or more routes have a degraded performance.

Paragraph 26. A method according to any of paragraphs 21 to 24, comprising updating, on a basis of the status of the one or more routes, a routing table maintained at either the communications node or the donor communications node to include an indication of which radio communications links have degraded performance.

Paragraph 27. A method according to any of paragraphs 21 to 26, comprising adjusting, on a basis of the status of the one or more routes, one or more of a measurement configuration, reporting conditions and handover conditions for the communications node.

Paragraph 28. A controlling communications node for communicating in a wireless backhaul network in a wireless communications network, the controlling communications node comprising: receiver circuitry configured to receive signals; transmitter circuitry configured to transmit signals; controller circuitry configured in combination with the transmitter circuitry to transmit, from the controlling communications node, a measurement configuration message to one or more other communications nodes in the wireless backhaul network formed by a plurality of communications nodes comprising the controlling communications node and at least the one or more other communications nodes, the measurement configuration message identifying measurement reporting trigger conditions for each of the one or more other communications nodes which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected, the wireless backhaul network being configured to communicate data from a core network of the wireless communications network for transmitting to one or more communications devices or to communicate data to the core network received from the one or more communications devices, at least one of the plurality of communications nodes being a donor communications node having a physical connection to the core network and providing communications resources for the plurality of communications nodes to form the wireless backhaul network, wherein the controller circuitry is configured to configure, in response to receiving measurements from one or more other communications nodes which received the measurement configuration, a reconfiguration message including one or more handover trigger conditions set by the controlling communications node to control a handover of the one or more communications nodes from which measurements were received to one or more others of the plurality of communications nodes from which radio signals can be detected in which the handover results in a change of network topology of the wireless backhaul network to communicate the data received from the core network to the one or more communications devices or to communicate the data received from the one or more communications devices to the core network, wherein the controller circuitry is configured in combination with the transmitter circuitry to arrange for the reconfiguration message to be transmitted to the one or more other communications nodes from which measurements were received.

Paragraph 29. A controlling communications node according to paragraph 28, wherein the measurement reporting trigger conditions for each of the one or more other communications nodes which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected comprise an absolute threshold of a measured signal parameter of one or more component carriers for the one or more others of the plurality of communications nodes from which radio signals can be detected. Paragraph 30. A controlling communications node according to paragraphs 28 or 29, wherein the measurement reporting trigger conditions for each of the one or more other communications nodes which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected comprise a difference in a measured signal parameter of one or more component carriers of the one or more others of the plurality of communications nodes from which radio signals can be detected with respect to the measured signal parameter a current communication node.

Paragraph 31. A controlling communications node according to paragraphs 28, 29 or 30, wherein the measurement reporting trigger conditions for each of the one or more other communications nodes which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected comprise a first absolute threshold of a measured signal parameter of one or more component carriers for the one or more others of the plurality of communications nodes from which radio signals can be detected and a second absolute threshold of a measured signal parameter of one or more component carriers of the current communications node.

Paragraph 32. A controlling communications node according to any of paragraphs 28 to 31, wherein the absolute threshold is a pre-defined threshold of one or more of a received signal strength indicator (RSSI), reference signal received power (RSRP) and/or a reference signal received quality (RSRQ) of the one or more component carriers for the one or more others of the plurality of communications nodes from which radio signals can be detected.

Paragraph 33. A controlling communications node according to any of paragraphs 28 to 32, wherein the receiver circuitry is configured in combination with the controller circuitry to receive, from a first of the one or more other communications nodes which received the measurement configuration message, a measurement report providing an indication of measurements of radio signals received from a second of the one or more others of the plurality of communications nodes from which radio signals can be detected. Paragraph 34. A controlling communications node according to any of paragraphs 28 to 33, wherein transmitting from the controlling communications node a measurement configuration message to one or more other communications nodes in the wireless backhaul network comprises transmitting the measurement configuration message from a central unit (CU) of the controlling node to a distributed unit (DU) via FI Application Protocol (F1AP) signalling; and transmitting the measurement configuration message from the DU to a Mobile Terminal (MT) of a first communications node of the one or more other communications nodes in the wireless backhaul network via RRC signalling.

Paragraph 35. A controlling communications node according to any of paragraphs 28 to 34, wherein the controlling node is the donor node having the physical connection to the core network and providing the radio resources for the plurality of communications nodes in the wireless backhaul network.

Paragraph 36. A communications node for communicating in a wireless backhaul network in a wireless communications network, the communications node comprising receiver circuitry configured to receive signals; transmitter circuitry configured to transmit signals; controller circuitry configured to determine based on one or more pre-defined conditions, whether a status of one or more routes in the wireless backhaul network for communicating data between one or more communications devices and a core network of the wireless communications network should be checked, the wireless backhaul network comprising the communications node, a first set of communications nodes and a donor communications node having a physical connection to the core network and providing radio resources to the communications node and the first set of communications nodes, wherein at least one of the routes comprises a radio communications link between the communications node and a first intermediate communications node of the first set upstream of the communications node and a radio communications link between the donor communications node and either the first intermediate communications node or a second intermediate communications node of the first set upstream from the communications node, wherein the controller circuitry is configured in combination with the transmitter circuitry to transmit, to the donor communications node, a route status check request requesting the donor communications node to check the status of the one or more routes, the status of the one or more routes being used by the donor communications node to determine whether the communications node should handover to one of the first set of communications nodes other than the first intermediate communications node or to arrange a handover of one of the first set of communications nodes to another of the first set of communications nodes in which the handover results in a change of network topology of the wireless backhaul network to communicate the data between the one or more communications devices and the core network.

Paragraph 37. A communications node according to paragraph 36, wherein the receiver circuitry is configured in combination with the controller circuitry to receive a command from the donor communications node to handover from a first attachment point to the first intermediate communications node which is currently being used to communicate the data via the radio communications link between the communications node and the first intermediate node to a second attachment point providing a radio link between the communications node and one of the first set of communications nodes other than the first intermediate communications node.

Paragraph 38. A communications node according to paragraph 37, wherein the command received from the donor communications node to handover includes a configuration for the handover.

Paragraph 39. A communications node according to paragraphs 36 to 38, wherein the one or more pre defined conditions include a detection, by the communications node, of one or more of: an amount of data in a buffer of the communications node exceeding a buffer capacity of the communications node, one or more routes in a routing table maintained at the communications node have a common hop or a performance degradation, data with a stringent Quality of Service (QoS) requirement being received at the communications node, a change in a mobility status of the communications node.

Paragraph 40. A communications node according to any of paragraphs 36 to 39, wherein the route status check request includes one or more of an indication of which routes should be checked, an indication of one or more pre-defined condition which caused the request to be transmitted, a measurement report.

Paragraph 41. A communications node for communicating in a wireless backhaul network in a wireless communications network, the communications node comprising receiver circuitry configured to receive signals; transmitter circuitry configured to transmit signals; controller circuitry configured in combination with the receiver circuitry to receive from a controlling communications node a measurement configuration message, the wireless backhaul network being formed by a plurality of communications nodes comprising the communications node which received the measurement configuration message and the controlling node, the measurement configuration message identifying measurement reporting trigger conditions for the communications node which received the measurement configuration message to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected, the wireless backhaul network being configured to communicate data from a core network of the wireless communications network for transmitting to one or more communications devices or to communicate data to the core network received from the one or more communications devices, at least one of the plurality of communications nodes being a donor communications node having a physical connection to the core network and providing communications resources for the plurality of communications nodes to form the wireless backhaul network; receive a reconfiguration message including one or more handover trigger conditions set by the controlling communications node to control a handover of the communications node which received the measurement configuration to one or more others of the plurality of communications nodes from which radio signals can be detected in which the handover results in a change of network topology of the wireless backhaul network to communicate the data received from the core network to the one or more communications devices or to communicate the data received from the one or more communications devices to the core network.

Paragraph 42. A communications node according to paragraph 41, wherein the measurement trigger conditions for the communications node to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected comprise an absolute threshold of a measured signal parameter of one or more component carriers for the one or more others of the plurality of communications nodes from which radio signals can be detected.

Paragraph 43. A communications node according to paragraphs 41 or 42, wherein the measurement reporting trigger conditions for the communications node to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected comprises a difference in a measured signal parameter of one or more component carriers of the one or more others of the plurality of communications nodes from which radio signals can be detected with respect to the measured signal parameter a current communication node.

Paragraph 44. A communications node according to paragraphs 41, 42 or 43, wherein the measurement reporting trigger conditions for the communications node to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected comprise a first absolute threshold of a measured signal parameter of one or more component carriers for the one or more others of the plurality of communications nodes from which radio signals can be detected and a second absolute threshold of a measured signal parameter of one or more component carriers of the current communications node.

Paragraph 45. A communications node according to any of paragraphs 41 to 44, wherein the absolute threshold is a pre-defined threshold of one or more of a received signal strength indicator (RSSI), reference signal received power (RSRP) and/or a reference signal received quality (RSRQ) of the one or more component carriers for the one or more others of the plurality of communications nodes from which radio signals can be detected.

Paragraph 46. A communications node according to any of paragraphs 41 to 45, wherein the controller circuitry is configured to determine whether or not the measurement reporting trigger conditions for the communications node to report measurements of radio signals received from one or more others of the plurality communications nodes from which radio signals can be detected included in the measurement configuration received from the controlling communications node are met, and if the trigger conditions are met, and the controller circuitry is configured in combination with the transmitter circuitry to transmit a measurement report to the controlling communications node.

Paragraph 47. A communications node according to any of paragraphs 41 to 46, wherein the controlling node is the donor node having the physical connection to the core network and providing the radio resources for the plurality of communications nodes in the wireless backhaul network.

Paragraph 48. A donor communications node for communicating in a wireless backhaul network in a wireless communications network, the donor communications node comprising receiver circuitry configured to receive signals; transmitter circuitry configured to transmit signals; controller circuitry configured in combination with the receiver circuitry to receive, from a communications node, a route status check request requesting the donor communications node to check a status of one or more routes in the wireless backhaul network for communicating data between one or more communications devices and a core network of the wireless communications network, the wireless backhaul network comprising the communications node, a first set of communications nodes and the donor communications node, the donor communications node having a physical connection to the core network and providing radio resources to the communications node and the first set of communications nodes, wherein at least one of the routes comprises a radio communications link between the communications node and a first intermediate communications node of the first set upstream of the communications node and a radio communications link between the donor communications node and either the first intermediate communications node or a second intermediate communications node of the first set upstream from the communications node, wherein the controller circuitry is configured to check the status of the one or more routes requested in the route status check request; using the status of the one or more routes to determine whether the communications node should handover to one of the first set of communications nodes other than the first intermediate communications node or to arrange a handover of one of the first set of communications nodes to another of the first set of communications nodes in which the handover results in a change of network topology of the wireless backhaul network to communicate the data between the one or more communications devices and the core network.

Paragraph 49. A donor communications node according to paragraph 48, wherein the controller circuitry is configured in combination with the transmitter circuitry to transmit a command to the communications node to handover from a first attachment point to the first intermediate communications node which is currently being used to communicate the data via the radio communications link between the communications node and the first intermediate node to a second attachment point providing a radio link between the communications node and one of the first set of communications nodes other than the first intermediate communications node.

Paragraph 50. A donor communications node according to paragraph 49, wherein the controller circuitry is configured in combination with the transmitter circuitry to transmitting a command to one of the first set of communications nodes to handover to another of the first set of communications nodes

Paragraph 51. A donor communications node according to any of paragraphs 48 to 50, wherein the route status check request includes one or more of an indication of which routes should be checked, an indication of one or more pre-defined conditions which caused the request to be transmitted, and a measurement report.

Paragraph 52. A donor communications node according to any of paragraphs 48 to 51, wherein the controller circuitry is configured to determine that a performance of one or more radio communications links on the one or more routes have a degraded performance.

Paragraph 53. A donor communications node according to any of paragraphs 48 to 52, wherein the controller circuitry is configured to update, on a basis of the status of the one or more routes, a routing table maintained at either the communications node or the donor communications node to include an indication of which radio communications links have degraded performance.

Paragraph 54. A donor communications node according to any of paragraphs 48 to 53, wherein the controller circuitry is configured to adjust, on a basis of the status of the one or more routes, one or more of a measurement configuration, reporting conditions and handover conditions for the communications node.

Paragraph 55. A system comprising a controlling communications node according to paragraph 28 and a communications node according to paragraph 41.

Paragraph 56. A system comprising a communications node according to paragraph 36 and a donor communications node according to paragraph 48.

Paragraph 57. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of any of paragraphs 1, 9, 14 and 21.

Described embodiments may be implemented in any suitable form including hardware, software, firmware or any combination of these. Described embodiments may optionally be implemented at least partly as computer software running on one or more data processors and/or digital signal processors. The elements and components of any embodiment may be physically, functionally and logically implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the disclosed embodiments may be implemented in a single unit or may be physically and functionally distributed between different units, circuitry and/or processors.

Although the present disclosure has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in any manner suitable to implement the technique. References

[1] Holma H. and Toskala A, “LTE for UMTS OFDMA and SC-FDMA based radio access”, John Wiley and Sons, 2009.

[2] RP-161901, “Revised work item proposal: Enhancements of NB-IoT”, Huawei, HiSilicon, 3GPP TSG RAN Meeting #73, New Orleans, USA, September 19 - 22, 2016.

[3] RP-170831, “New SID Proposal: Study on Integrated Access and Backhaul for NR”, AT&T, 3GPP RAN Meeting #75, Dubrovnik, Croatia, March 2017.

[4] 3GPP TTR 38.874 “3 ^rd Generation Partnership Project; Technical Specification Group Radio Access Network; Study on Integrated Access and Backhaul; (Release 15)”, 3 ^rd Generation Partnership Project, February 2018.

[5] R2-1801606, “Proposals on IAB Architecture”, Qualcomm et al, 3GPP TSG-RAN WG2 NR Ad hoc 1801, Vancouver, Canada, January 22 - 26, 2018.

[6] R3-181502, “Way Forward - IAB Architecture for F2/3 relaying”, Qualcomm et al, 3GPP TSG- RAN WG3 Meeting #99, Athens, Greece, February 26 - March 2, 2018.