Methods, communications devices, transmission and reception points, and uplink-only reception points

Abstract

A method of operating a communications device is provided. The method comprises receiving, from a transmission and reception point, TRP, of a heterogeneous communications network, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP. The URP is configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link. The TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP. The URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell. The URP is unable to transmit downlink transmissions to the communications device. The method comprises determining, based on the assistance signal, to form the wireless communications link with the URP. The method comprises forming the wireless communications link with the URP, the forming the wireless communications link with the URP comprising transmitting a synchronisation signal to the URP.

Description

[0001] METHODS, COMMUNICATIONS DEVICES, TRANSMISSION AND RECEPTION POINTS, AND UPLINK-ONLY RECEPTION POINTS

[0002] BACKGROUND

[0003] Field of Disclosure

[0004] The present disclosure relates to communications devices, transmission and reception points (TRPs) and uplink-only reception points (URPs) of a heterogeneous communications network, and methods of operating communications devices, TRPs and URPs of a heterogonous communications network.

[0005] The present application claims Paris convention priority from EP patent application number 23193599.0, filed on 25 August 2023, the contents of which are hereby incorporated by reference in their entirety.

[0006] Description of Related Art

[0007] 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.

[0008] Modern mobile telecommunication systems, such as those based on the 3GPP defined UMTS and Long Term Evolution (LTE) architecture, 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. 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, is expected to continue to increase rapidly.

[0009] Wireless communications networks are expected to routinely and efficiently support communications with an ever-increasing range of devices associated with a wide range of data traffic profiles and types. For example, it is expected that wireless communications networks 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. Other types of device, for example supporting high-definition video streaming, may be associated with transmissions of relatively large amounts of data with relatively low latency tolerance. Other types of device, for example used for autonomous vehicle communications and for other critical applications, may be characterised by data that should be transmitted through the network with low latency and high reliability. A single device type might also be associated with different traffic profiles I characteristics depending on the application(s) it is running. For example, different consideration may apply for efficiently supporting data exchange with a smartphone when it is running a video streaming application (high downlink data) as compared to when it is running an Internet browsing application (sporadic uplink and downlink data) or being used for voice communications by an emergency responder in an emergency scenario (data subject to stringent reliability and latency requirements). In view of this there is a desire for current generation wireless communications networks, for example those referred to as 5G or new radio (NR) systems I new radio access technology (RAT) systems, as well as future iterations I releases of existing systems, to efficiently support connectivity for a wide range of devices associated with different applications and different characteristic data traffic profiles and requirements.

[0010] 5G NR has continuously evolved and the current work plan includes 5G-NR-advanced in which some further enhancements are expected, especially to support new use- cases / scenarios with higher requirements. The desire to support these new use-cases and scenarios gives rise to new challenges for efficiently handling communications in wireless communications systems that need to be addressed.

[0011] SUMMARY OF THE DISCLOSURE

[0012] The present disclosure can help address or mitigate at least some of the issues discussed above.

[0013] Various aspects and features of the present disclosure are defined in the appended claims.

[0014] 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.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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:

[0017] Figure 1 schematically represents some aspects of an LTE-type wireless telecommunication system which may be configured to operate in accordance with certain embodiments of the present disclosure;

[0018] Figure 2 schematically represents some aspects of a new radio access technology (RAT) wireless telecommunications system which may be configured to operate in accordance with certain embodiments of the present disclosure;

[0019] Figure 3 is a schematic block diagram of an example infrastructure equipment and communications device which may be configured to operate in accordance with certain embodiments of the present disclosure;

[0020] Figure 4 schematically represents an example of a Heterogeneous Network (HetNet);

[0021] Figure 5 schematically represents an example of a HetNet including a plurality of uplink-only reception points (URPs);

[0022] Figure 6 schematically illustrates an example of conventional 4-step RACH;

[0023] Figure 7 schematically illustrates an example of conventional 2-step RACH;

[0024] Figure 8 is a method of operating a communications device in accordance with example embodiments; Figure 9 is a method of operating a communications device in accordance with example embodiments;

[0025] Figure 10 schematically illustrates an example of a heterogeneous network in accordance with example embodiments;

[0026] Figure 11 schematically illustrates slot timing relations between the TRP, UE and URP of Figure 10 in accordance with example embodiments.

[0027] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] Long Term Evolution Advanced Radio Access Technology (4G)

[0029] 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.

[0030] 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.

[0031] Data is transmitted from base stations 1 to communications devices or mobile terminals (MT) 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. The communications or terminal devices 4 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.

[0032] 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.

[0033] New Radio Access Technology (5G (NR))

[0034] An example configuration of a wireless communications network which uses some of the terminology proposed for and used in NR and 5G is shown in Figure 2. In Figure 2 a plurality of transmission and reception points (TRPs) 10 are connected to distributed control units (Dlls) 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 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.

[0035] 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.

[0036] The TRPs 10 of Figure 2 may in part have a corresponding functionality to a base station or eNodeB of an LTE network. Similarly, the communications devices 14 may have a functionality corresponding to the UE devices 4 known for operation with an LTE network. It will be appreciated therefore that operational aspects of a new RAT network (for example in relation to specific communication protocols and physical channels for communicating between different elements) may be different to those known from LTE or other known mobile telecommunications standards. However, it will also be appreciated that each of the core network component, base stations and communications devices of a new RAT network will be functionally similar to, respectively, the core network component, base stations and communications devices of an LTE wireless communications network.

[0037] 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 I TRPs 10 may be broadly considered to provide functionality corresponding to the base stations 1 of Figure 1. The term network infrastructure equipment I 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 I central unit and I or the distributed units I 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 12 via one of the distributed units I TRPs 10 associated with the first communication cell 12.

[0038] 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.

[0039] Thus, certain embodiments of the disclosure as discussed herein may be implemented in wireless telecommunication systems I 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 I access nodes and a communications device, wherein the specific nature of the network infrastructure equipment I 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 I 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 I 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.

[0040] 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 circuit 49, a receiver circuit 48 and a controller circuit 44 which is configured to control the transmitter circuit 49 and the receiver circuit 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 circuit 30 and received by the receiver circuit 48 in accordance with the conventional operation.

[0041] The transmitter circuits 30, 49 and the receiver circuits 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 controller circuits 34, 44 (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. The transmitters, the receivers and the controllers are schematically shown in Figure 3 as separate elements for ease of representation. However, it will be appreciated that the functionality of these elements can be provided in various different ways, for example using one or more suitably programmed programmable computer(s), or one or more suitably configured application-specific integrated circuit(s) I circuitry I chip(s) I chipset(s). As will be appreciated the infrastructure equipment I TRP I base station as well as the UE I communications device will in general comprise various other elements associated with its operating functionality.

[0042] 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.

[0043] The interface 46 between the DU 42 and the CU 40 is known as the F1 interface which can be a physical or a logical interface. The F1 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 or wireless 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 TRP10 to the DU 42 and the F1 interface 46 from the DU 42 to the CU 40. Although Figures 2 and 3 illustrate the TRP 10 as a separate object to the DU 42 and the CU 40, the TRP may alternatively comprise the DU 42 and / or CU 40. The term “TRP” may be used interchangeably with “gNB”.

[0044] 5G / NR radio access technologies can provide various functionalities such as Massive Machine Type Communications (mMTC), enhanced Mobile Broadband (eMBB) and Ultra Reliable & Low Latency Communications (URLLC). mMTC are devices such as sensors that have low complexity and a large coverage density of 1 million devices per km2. eMBB services are characterised by high capacity with a requirement to support up to 20 Gb / s. Furthermore, URLLC requires a reliability of 1 - 10'5(99.999%) to 1 - 10'6(99.9999%) for one transmission of a 32-byte packet with a user plane latency of 1ms.

[0045] 3GPP has already completed the first phase of 5G (known as 5G-NR) in Release-15, 16 and 17 of the 3GPP standards. In the first phase, 3GPP has specified features to bring about mMTC, eMBB, URLLC and other functionalities such as massive multiple-input multiple-output (MIMO), reduced complexity UEs and coverage enhancements.

[0046] 3GPP is now moving ahead with a second phase of 5G (known as 5G-NR-Advanced) in Release 18, 19 of the 3GPP standards, and beyond. One feature being proposed in the second phase is heterogeneous networks (HetNets) and, in particular, heterogeneous networks with uplink-only reception points (URPs).

[0047] Heterogeneous Network (HetNet)

[0048] In a 5G operation, a Heterogeneous Network (HetNet) may be deployed. A HetNet is a network comprising a plurality of TRPs including a TRP which provides a larger cell and one or more TRPs which provide a respective one or more smaller cells within the larger cell. The larger cell may be a “macro cell”, for example. A TRP which provides a macro cell may alternatively be referred to as a “macro TRP” or “macro gNB”. The macro TRP may be connected to a core network via a DU and a CU (as shown in Figures 2 and 2). In some cases, the TRP may comprise the DU and CU. As will be known to one skilled in the art, a TRP providing a macro cell transmits with a higher power than a TRP providing a small cell. Therefore, a macro cell provides a larger coverage area for UEs than a small cell. As will be understood by a person skilled in the art, small cells are typically provided to alleviate a load on the TRP which provides the macro cell caused by uplink and downlink traffic. This is particularly advantageous when there is a large number of UEs present in the macro cell (referred to as “dense macro cell deployment”). Furthermore, TRPs providing small cells may be deployed near the edge of the macro cell to enhance coverage near the cell edge. An example of a HetNet is schematically illustrated in Figure 4.

[0049] As shown in Figure 4, a first TRP 402 provides a macro cell 404 for a first UE 424, a second UE 426, a third UE 428 and a fourth UE 430 located within the macro cell 404. Also shown is a second TRP 406 providing a small cell 408 for the first UE 424 which is located within the small cell 408 provided by the second TRP 406. Also shown is a third TRP 414 providing a small cell 416 for the third UE 428 which is located within the small cell 416 provided by the third TRP 414. The second UE 426 and the fourth UE 430 are located within the macro cell 404 but are not located within the small cell 408 provided by the second TRP 406 or the small cell 416 provided by the third TRP 414.

[0050] Although not shown in Figure 4, the second TRP 406 and the third TRP 414 may be connected to the first TRP 402 via wired backhaul connections such as fibre optic cables or wireless connections, thereby allowing communication between the first TRP 402 and the second TRP 406 and between the first TRP 402 and the third TRP 414. When the second TRP 406 and the third TRP 414 are connected to the first TRP 402, scheduling may be coordinated and multi-TRP MIMO may be provided.

[0051] A technical problem associated with HetNets is that UEs, particularly those near the edge of a small cell, may experience significant downlink interference from the TRP which provides the macro cell. For example, as shown in Figure 4, the first UE 424 is located near the edge of the small cell 408 provided by the second TRP 406. The first UE 424 is receiving a downlink transmission 420 from the second TRP 406. At the same time, the second UE 418 is receiving a downlink transmission 418 from the first TRP 402. Since the first UE 424 is near the edge of the small cell 408 provided by the second TRP 406, a power of the downlink transmission 420 from the second TRP 406 is likely to be lower than a power of the downlink transmission 418 from the first TRP 402 at the location of the first UE 424. Therefore, the downlink transmission 418 from the first TRP 402 causes significant interference 418a to the downlink transmission from the second TRP 406.

[0052] Similarly, UEs being served by the TRP providing the macro cell may experience significant downlink interference from UEs being served by a TRP providing a small cell. For example, as shown in Figure 4, the fourth UE 430 is located near the edge of the macro cell 404 provided by the first TRP 402. The fourth UE 430 is receiving a downlink transmission 432 from the first TRP 402. At the same time, the third UE 428 is receiving a downlink transmission 422 from the third TRP 414. Since the fourth UE 430 is near the edge of the macro cell 404 provided by the first TRP 402, a power of the downlink transmission 432 from the first TRP 402 is likely to be lower than a power of the downlink transmission 422 from the third TRP 414 at the location of the fourth UE 430. Therefore, the downlink transmission 422 from the third TRP 414 causes significant interference 422a to the downlink transmission 432 from the first TRP 402.

[0053] On the other hand, uplink interference may also be experienced in HetNet deployments. For example, interference may occur between an uplink transmission from a UE to a TRP providing a small cell and an uplink transmission from another UE to a TRP providing a macro cell, or another small cell. However, uplink interference can typically be reduced by one of the UEs reducing a transmission power of its uplink transmission.

[0054] Uplink-only reception point (URP)

[0055] It has been observed that there is often a bottleneck of uplink traffic in dense macro cell deployments. The load caused by the uplink traffic on the TRP providing the macro cell can be alleviated by providing a HetNet deployment such as that described with reference to Figure 4. However, as described above, such networks can present significant problems due to downlink interference. Recognising this, it has been proposed to introduce uplink-only reception points (URP) in HetNets ([2]). URPs are configured to receive uplink transmissions from UEs but cannot transmit downlink transmissions to UEs. A URP may be connected to a TRP providing a macro cell via a wired backhaul connection, such as a fibre optic cable, thereby allowing communication between the URP and the TRP providing the macro cell. By deploying URPs in a HetNet, the load on the TRP providing the macro cell can be alleviated and the downlink interference which would otherwise be experienced, or caused, by TRPs providing small cells can be prevented. However, URPs are not able to alleviate the load on the TRP providing the macro cell caused by downlink transmissions. URPs deployed near the macro cell edge may increase the throughput of a UE being served by that URP because the UE may be close to the URP and therefore likely have better radio conditions with the URP compared to the TRP providing the macro cell. Furthermore, UEs near the macro cell edge may transmit uplink transmissions to the URP with a lower transmission power than a transmission power with which the UE transmits uplink transmissions to the TRP providing the macro cell, which results in reduced uplink interference. Furthermore, URPs can be low cost because they do not require a wireless transmitter for communicating downlink transmissions to UEs. URPs may also help replace dual connectivity (DC) and solve uplink problems such as traffic split ratio and power sharing in DC scenarios. Traffic split ratios and power sharing are typically semi statically configured in DC, but they may be dynamically configured if URPs are used.

[0056] An example of a HetNet which includes URPs is shown in Figure 5. As shown in Figure 5, a first TRP 502 provides a macro cell 504 for a first UE 534, a second UE 536, a third UE 538 and a fourth UE 540 located within the macro cell 504. Also shown is a first URP 506 providing a small cell 508 for the first UE 534 which is located within the small cell 508 provided by the first URP 506. Also shown is a second URP 510 providing a small cell 512 for the third UE 538 which is located within the small cell 512 provided by the second URP 510. Also shown is a second TRP 514 providing a small cell 516 for the fourth UE 540 which is located within the small cell 516 provided by the second TRP 514. The second UE 536 is located within the macro cell 504 but is not located within the small cell 508 provided by the first URP, the small cell 512 provided by the second URP 510 or the small cell 516 provided by the second TRP 514.

[0057] Since the first UE 534 is located within the macro cell 504 provided by the first TRP 502 and the small cell 508 provided by the first URP 506, then the first UE 534 is served by the first URP 506 for uplink transmissions 520 and is served by the first TRP 502 for downlink transmissions 518. In other words, the first UE 534 is able to transmit uplink transmissions 520 to the first URP 506 and receive downlink transmissions 518 from the first TRP 502.

[0058] Since the second UE 536 is within the macro cell 504 provided by the first TRP 502 but is not located within the small cell 508 provided by the first URP, the small cell 512 provided by the second URP 510 or the small cell 516 provided by the second TRP 514, then the second UE 536 is served by the first TRP 502 for uplink transmissions 522 and downlink transmissions 524. In other words, the second UE 536 is able to transmit uplink transmissions 522 to the first TRP 502 and receive downlink transmissions 524 from the first TRP 502.

[0059] Since the third UE 538 is located within the macro cell 504 provided by the first TRP 502 and the small cell 512 provided by the second URP 510, then the third UE 538 is served by the second URP 510 for uplink transmissions 528 and is served by the first TRP 502 for downlink transmissions 526. In other words, the third UE 538 is able to transmit uplink transmissions 528 to the second URP 510 and receive downlink transmissions 526 from the first TRP 502. Since the fourth UE 540 is located within the small cell 516 provided by the second TRP 514, then the fourth UE 540 is served by the second TRP 514 for uplink transmissions 532 and for downlink transmissions 530. In other words, the fourth UE 540 is able to transmit uplink transmissions 532 and receive downlink transmissions 530 from the second TRP 514.

[0060] Although not shown in Figure 5, the first URP 506, second URP 510 and second TRP 514 may be connected to the first TRP 502 via a wired backhaul connections, such as fibre optic cables, thereby allowing communication between the first URP 506, second URP 510, second TRP 514 and the first TRP 502

[0061] Determining Timing Advance (TA) during Initial Access

[0062] In existing wireless communications networks, a UE performs an initial access procedure with a gNB to transition from a Radio Resource Control (RRC) idle state, or RRC inactive state, to an RRC connected state. During initial access, the UE follows either a 4-step random access channel (RACH) procedure or a 2-step RACH procedure. A conventional 4-step RACH procedure is shown in Figure 6.

[0063] In a first step, a UE 602 transmits a physical random-access channel (PRACH) preamble to a gNB 604 (“Message 1”). Based on the received PRACH preamble, the gNB 604 estimates a one-way propagation delay between the UE 602 and the gNB 604. The gNB 604 then converts the estimated propagation delay into a timing advance (TA) value (which may be referred to as a “two-way propagation delay”).

[0064] In a second step, the gNB 604 transmits a random-access response (RAR) to the UE 602 using a Random Access Ratio Network Temporary Identifier (RA-RNTI) (“Message 2”). The RAR message comprises a detected index of the PRACH preamble, the TA value and a resource allocation for a physical uplink shared channel (PUSCH) transmission to be transmitted by the UE 602 (Message 3). The UE 602 adjusts its future uplink transmissions based on the TA value.

[0065] In a third step, the UE 602 transmits an identification of the UE 602 in the PUSCH transmission for which the resource allocation was received (“Message 3”).

[0066] In a fourth step, the gNB 604 transmits a contention-resolution message to the UE 602 comprising a confirmation of the identification of the UE 602 that is being connected to a cell provided by the gNB 604 (“Message 4”). This resolves contention if, for example, multiple UEs transmitted a PRACH preamble to the gNB 604 in the first step.

[0067] A conventional 2-step RACH procedure is shown in Figure 7.

[0068] In a first step, a UE 702 transmits msgA to a gNB 704. msgA comprises a PRACH preamble and a PUSCH which comprises data for the gNB 704. Based on msgA, the gNB 704 estimates a one-way propagation delay between the UE 702 and the gNB 704. The gNB 704 then converts the estimated propagation delay into a timing advance (TA) value (two-way propagation delay). Therefore, msgA is similar to Message 1 and Message 3 in 4-step RACH.

[0069] In a second step, the gNB 704 transmits msgB to the UE 702 using a msgB-RNTI. msgB comprises responses to one or more UEs. In case msgA was successful for a given UE, msgB comprises at least a contention resolution identity (ID), a cell Radio Network Temporary Identifier (C-RNTI) and the TA value. Therefore, msgB is similar to Message 2 and 4 in 4-step RACH. The UE adjusts its future uplink transmissions based on the TA value.

[0070] For both 4-step and 2-step RACH, the TA value (denoted as TA) is a value in the following sequence: 0, 1 , 2, 3... , 3846. The UE 602, 702 converts the TA value into an absolute time value in “seconds” using the following equation: TTA= TA• 16 • 64 • rc / 2^, where p is the subcarrier spacing index as shown on Table 1 , and Tcis the basic timing unit defined in [3]

[0071] Table 1

[0072] 5G / NR Discovery and Synchronisation Procedures

[0073] In some scenarios in conventional HetNets, it is beneficial for a UE to handover from a TRP providing a macro cell to a TRP providing a small cell or vice versa. For example, for a given UE location, a particular TRP may provide a better signal strength than other TRPs. In order to decide whether to perform a handover, the UE typically receives downlink signals from each of the TRPs in a HetNet and measures a signal strength of each of the downlink signals. The UE then decides to form a wireless communications link with the TRP which transmitted the downlink signal with the highest signal strength. During the formation of the wireless communications link, the UE synchronises with the TRP. The UE receives a downlink synchronization signal block (SSB) from the TRP and uses this to perform downlink synchronisation with the TRP. After downlink synchronisation, the UE receives system information comprising a UL bandwidth part (BWP) and random-access resources for uplink synchronisation. The UE transmits a PRACH preamble using the RACH resources to the TRP. The TRP determines a one-way propagation delay between the TRP and the UE and, because uplink reception and downlink transmission are co-located on the TRP, the TRP also works out the timing advance (also known as the round trip time or two-way propagation delay) by multiplying the one-way propagation delay by two. The timing advance is then transmitted to the UE to complete uplink synchronisation.

[0074] However, technical challenges arise in efficiently forming wireless communications links with URPs in a HetNet because URPs are unable to transmit downlink transmissions and, therefore, uplink and downlink transmissions are not co-located on a URP. The UE is faced with technical problems, firstly, in determining whether to form a wireless communications link with a URP because the UE cannot receive downlink signals from the URP to measure for received signal strength and, secondly, in synchronising uplink transmissions between the UE and the URP because uplink reception and downlink transmission are not co-located.

[0075] There is therefore a need for methods, communications devices, TRPs and URPs which can address the above problems.

[0076] Figure 8 illustrates a method operating a communications device in accordance with example embodiments. The method starts in step S1.

[0077] In step S2, the method comprises receiving, from a transmission and reception point, TRP, of a heterogeneous communications network, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP. The URP is configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link. The TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP. The URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell. The URP is unable to transmit downlink transmissions to the communications device. In some embodiments, the uplink-only cell is located within the cell provided by the TRP. In some embodiments, the uplink only cell is smaller than the cell provided by the TRP. In some embodiments, the uplink-only cell is smaller than, and located within, the cell provided by the TRP.

[0078] The communications device may be a UE, for example.

[0079] The TRP may be a macro-TRP (or macro gNB) providing a macro-cell, for example. Although, it will be appreciated that the TRP is not required to be a macro-TRP but may be any TRP which is connected to the URP via a backhaul communications link.

[0080] In some embodiments, the TRP and URP may be synchronised in time. For example, the TRP and URP may be synchronised at a slot, subframe, or radio frame level. In some embodiments, the TRP and the URP are not synchronised in time, but are offset in time by a known offset.

[0081] In some embodiments, the TRP and the URP use a same carrier frequency. In other embodiments, the TRP and the URP use different carrier frequencies. The UE may be preconfigured to know the carrier frequency used by the URP.

[0082] In some embodiments, the assistance signal comprises an indication of a downlink received reference power threshold, RSRP, and the determining to form the wireless communications link with the URP comprises determining that an RSRP of a downlink signal received by the communications device from the TRP is below the downlink RSRP threshold. The low RSRP is an indication that the communications device is near an edge of the cell provided by the TRP, and therefore is likely close to the URP (particularly, in a dense cell deployment). In some embodiments, the assistance signal comprises, in addition to the RSRP threshold, one or more of an uplink bandwidth part or random-access resources for transmission of the synchronisation signal to the URP.

[0083] In some embodiments, the assistance signal comprises an instruction for the communications device to form the wireless communications link with the URP, and the determining to form the wireless communications link with the URP comprises identifying that the assistance signal comprises an instruction for the communications device to form the wireless communications link with the URP.

[0084] In some embodiments, the assistance signal is transmitted in system information block (SIB).

[0085] In step S3, the method comprises determining, based on the assistance signal, to form the wireless communications link with the URP.

[0086] In step S4, the method comprises forming the wireless communications link with the URP. The forming of the wireless communications link with the URP comprises transmitting a synchronisation signal to the URP.

[0087] The synchronisation signal may be a PRACH preamble or a Sounding Reference Signal, for example. In some embodiments, the forming of the wireless communications link may comprise handing over from communicating uplink transmissions with the TRP to communicating uplink transmissions with the URP. In some embodiments, the forming of the wireless communications link comprises performing initial access with the URP when the communications device is in an RRC idle or RRC inactive state with respect to the TRP.

[0088] The method ends in step S5.

[0089] By determining whether to form a wireless communications link with a URP based on an assistance signal received from a TRP, a communications device can efficiently establish a connection with a URP, and thereby alleviate a load on the TRP caused by uplink traffic, and efficiently establish a connection with a URP.

[0090] In the following description, the communications device will be referred to as a “UE”, but it will be appreciated that the UE may be any communications device. Furthermore, it will be appreciated that, in the following description, the TRP being referred to may be a macro TRP.

[0091] UE-initiated Synchronisation

[0092] Since URPs cannot transmit downlink signals to a UE, it is difficult for a UE to know whether it will be beneficial to attempt to form a wireless communications link with a URP. For example, it is difficult for a UE to know whether there are any URPs which are nearby the UE.

[0093] In some embodiments, the assistance signal comprises an indication of a received reference power threshold, RSRP, threshold. The UE may measure an RSRP of a downlink signal received from the TRP. If the measured RSRP of the downlink signal is below the received RSRP threshold, the UE may determine to form a wireless communications link with a URP. This recognises that, if the RSRP of the downlink signal is low, then the UE is likely near a cell edge of a cell provided by the TRP. Consequently, the UE is likely to be close to a URP which are often deployed near the edge of the cell provided by the TRP. Therefore, the URP is likely to be able to successfully receive uplink transmissions from the UE. Furthermore, if the UE is close to the URP, then the UE will be able to transmit uplink transmissions at a lower power (or higher modulation and coding scheme (MCS)) than the transmission power (or MCS) which was used for uplink transmissions to the TRP. The assistance signal comprising the RSRP threshold may be transmitted in system information (such as an SIB) in some embodiments.

[0094] In some cases, even though the RSRP of the downlink signal is below the RSRP threshold, there may not be a URP near-by the UE. Therefore, a scenario may arise where the UE determines that the RSRP of the downlink signal is below the RSRP threshold and transmits the synchronisation signal to the URP, even though the URP may not be near-by. In this case, since the URP is far away from the UE, the UE may not receive a response to the synchronisation signal from the TRP. For example, although the TRP may transmit a response to the synchronisation signal to the UE, the RSRP of the response at the location of the UE may be too low for the UE to detect. Therefore, in some embodiments, if the UE does not receive a response to the synchronisation signal from the TRP for a pre-defined time interval, then the UE will re-transmit the synchronisation signal to the URP. The pre-defined time interval may be transmitted by the TRP to the UE and may be included in the assistance signal. The retransmission of the synchronization signal to the URP may be transmitted at a higher power.

[0095] In some embodiments, the pre-defined time interval is a periodic time interval. In other words, the UE may periodically retransmit the synchronisation signal to the URP if the UE does not receive a response to the synchronisation signal from the TRP. Embodiments in which the UE implements the time interval, UE power consumption can be reduced compared to cases where the UE continuously monitors whether an RSRP of received downlink signals from the TRP fall below the RSRP threshold.

[0096] Network Initiated Synchronisation

[0097] In some embodiments, the TRP may determine that the UE should form a wireless communications link with a URP and, in response, includes an instruction in the assistance signal instructing the UE to form the wireless communications link with the URP. In some embodiments, the instruction in the assistance signal comprises a Physical Downlink Control Channel, PDCCH, order comprising an identification of the synchronisation signal to transmit to the URP.

[0098] In some embodiments, the UE receives a downlink signal from the TRP, measures an RSRP of the received downlink signal, and transmits an indication of the RSRP to the TRP. Then, based on the RSRP, the TRP determines that the UE should form a wireless communications link with a URP. For example, if the TRP determines that the RSRP is below a threshold, then the TRP transmits the assistance signal comprising the instruction to form a wireless communications link with the URP.

[0099] In some embodiments, the UE transmits, to the TRP, an indication of a location of the UE in the cell provided by the TRP. The TRP may determine that the UE should form a wireless communications link with a URP based on the indication of the location received from the UE.

[0100] In some embodiments, the UE may transmit, to the TRP, information regarding a nearest TRP to the UE. The TRP may determine that the UE should form a wireless communications link with a URP based on the information regarding the nearest TRP to the UE. For example, the UE may transmit one or more of an indication of a location of the nearest TRP, a downlink beam direction of the nearest TRP or an uplink beam direction of the nearest TRP.

[0101] In some embodiments, where the TRP and the URP operate in the same frequency of the uplink spectrum, the URP may receive uplink transmissions intended for the TRP (e.g., SRS). In such embodiments, the URP may forward an indication to the TRP that the URP received uplink transmissions from the UE. Based on this, the TRP may determine that the UE is close to the URP and therefore determines that the UE should form a wireless communications link with the URP.

[0102] Determining Timing Advance for a URP

[0103] Figure 9 illustrates a method of operating a communications device in accordance with example embodiments. The method starts in step S10.

[0104] In step S20, the method comprises determining to form a wireless communications link with an uplink-only reception point, URP, of a heterogeneous communications network for transmitting uplink transmissions to the URP.

[0105] For example, the communications device may determine to form a wireless communications link with the URP based on an assistance signal received from the TRP using any one of the methods previously discussed herein.

[0106] In other examples, the communications device may periodically, or at predefined time intervals, determine to form, or attempt to form, a wireless communications link with a URP.

[0107] In steps S30, S40 and S50, the method comprises forming the wireless communications link with the URP. In step S30, the forming the wireless communications link with the URP comprises transmitting a synchronisation signal to the URP.

[0108] In step S40, the forming of the wireless communications link with the URP comprises receiving, from a transmission and reception point, TRP, of the heterogeneous communications network a response to the synchronisation signal comprising an indication of a propagation delay between the URP and the communications device.

[0109] An “indication of a propagation delay” may be a one-way propagation delay or a two-way propagation delay (Timing Advance (TA)), for example.

[0110] In step S50, the forming the wireless communications link with the URP comprises using the indication of the propagation delay to synchronise a transmission time of each of the one or more uplink transmissions at the communications device with a reception time of each of the one or more uplink transmissions at the URP. The TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP. The URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell. The URP is unable to transmit downlink transmissions to the communications device. In some embodiments, the uplink-only cell is located within the cell provided by the TRP. In some embodiments, the uplink only cell is smaller than the cell provided by the TRP.

[0111] The method ends in step S60.

[0112] Therefore, in accordance with example embodiments, the communications device can receive the indication of the propagation delay between the communications device and the URP from the TRP and use this to synchronise uplink transmissions with the TRP. Consequently, embodiments can provide a way to efficiently synchronise uplink transmissions with URPs even though uplink and downlink transmissions are not co-located.

[0113] An example of determining a propagation delay between a UE and a URP will now be described with reference to Figures 10 and 11. In Figure 10, a UE 1004 is initially in an RRC connected mode with a TRP 1002 (such as a macro-TRP) and can therefore transmit uplink transmissions 1008 to the TRP 1002 and receive downlink transmissions 1012from the TRP. Although not shown, the UE 1004 is located within a cell provided by the TRP 1002. As shown in Figure 10, a URP 1006 is located nearby the UE 1004. The URP 1006 is connected to the TRP 1002 via a backhaul communications link (which may be a wired communications link, for example, such as a fibre optic cable). In the example shown in Figure 10, the URP 1006 and TRP 1002 are synchronised in time. The UE 1004 may determine to form a wireless communications link with the URP, for example, by using any of the methods of determining to form the wireless communications link with the URP 1006 discussed in this disclosure. As part of forming the wireless communications link with the URP 1006, the UE 1004 transmits a synchronisation signal 1010 to the URP 1006.

[0114] Figure 11 schematically illustrates propagation delays between the UE 1004, URP 1006 and TRP 1002 shown in Figure 10. As will be appreciated from Figure 11 , if the TRP 1002 transmits a downlink transmission in slot 1102, then the UE 1004 receives this downlink transmission in a slot 1104 which is delayed by tpifrom the slot 1102 in which the downlink transmission is transmitted. Therefore, the one-way propagation delay between the TRP 1002 and the UE 1004 is tpi. As shown in Figure 11 , a slot 1106 at the URP 1006 when the TRP 1002 transmits the downlink transmission to the UE 1004 is aligned with the slot 1102 at the TRP 1002. Therefore, the TRP 1002 and the URP 1006 are synchronised in time. As will be appreciated from Figure 11 , if the UE 1004 transmits an uplink transmission (such as a PRACH preamble) to the URP 1006 in a slot 1108, then the uplink transmission will be received at the URP 1110 in a slot 1110 which is delayed by tP2 from the slot 1108 at the UE 1004 in which the uplink transmission was transmitted. Therefore, a one-way propagation delay between the UE 1004 and the URP 1006 is tP2. Furthermore, a one-way propagation delay between the TRP 1002 and the URP 1006 via the UE 1004 is tpi+ tP2.

[0115] In accordance with example embodiments, the TRP 1002 may determine the one-way propagation delay tP2 between the UE 1004 and the URP 1006. For example, the TRP 1002 may determine tP2 based on Equation 1 below. tp2= (tpi+tp2) - (2*tpi) / 2 Equation 1.

[0116] The one-way propagation delay between the TRP 1002 and the UE 1004 (tpi) is known to the TRP 1002, for example, by employing a legacy RACH procedure, such as the procedure described with reference to Figure 6 or Figure 7. Furthermore, the one-way propagation delay, tpi+tP2, between the TRP 1002 and the URP 1006 via the UE 1004 is known to the URP 1006. For example, the URP 1006 may determine tpi+tP2 based on a time at which the synchronisation signal 1010 is received from the UE. In a particular example, the TRP 1002 may transmit an indication, to the URP 1006, of communications resources in which the communications device will transmit the synchronisation signal to the URP 1006. The URP 1006 may determine tpi+tP2 based on the indicated communications resources and the actual time of arrival of the synchronisation signal at the URP 1006. In accordance with example embodiments, the URP 1006 may transmit an indication of tpi+tP2 to the TRP 1002. Then, the TRP 1002 may determine tP2 using Equation 1. Then, the TRP 1002 may transmit, to the UE 1004, a response (such as a RAR) to the synchronisation signal 1010 comprising an indication of tP2 to the UE 1004. For example, indication of tP2 may be a TA based on the propagation delay between the UE 1004 and the URP 1006 (i.e., TA = 2*tP2).

[0117] In addition to transmitting an indication of tpi+tP2 to the TRP 1002, the URP 1006 may also transmit the synchronisation signal to the TRP 1002 and then the TRP 1002 may transmit a response to the synchronisation signal to the UE 1004. In some embodiments, the URP 1006 may transmit an indication of tpi+tP2 to the TRP 1002 and does not also transmit the synchronisation signal to the URP 1006.

[0118] Synchronisation Signal

[0119] In some embodiments, where the TRP and the URP operate using different carrier frequencies, the UE uses preconfigured transmission gaps when transmitting the synchronisation signal to the URP. In other words, the UE may transmit the synchronisation signal during pre-defined time intervals.

[0120] In some embodiments, the URP may measure a pathloss of the synchronisation signal received from the UE and transmit an indication of the pathloss of the synchronisation signal to the TRP. The TRP may then determine, based on the pathloss, whether or not the UE is permitted to form the wireless communications link with the URP.

[0121] PRACH Preamble

[0122] In some embodiments, as mentioned above, the synchronisation signal may be a PRACH preamble. In some embodiments, the TRP transmits an indication of a RACH configuration to the UE and the UE selects, based on the PRACH configuration, RACH resources for transmitting the PRACH preamble. This indication may be comprised in the assistance signal or transmitted as a separate signal.

[0123] In some embodiments, the TRP transmits, to the UE, an indication of a dedicated PRACH configuration and the UE selects RACH resources from the PRACH configuration for transmitting the PRACH preamble to the UE. In such cases, the indication may be comprised in a system information block (SIB) or Radio Resource Control (RRC) signal. This indication may be comprised in the assistance signal or transmitted as a separate signal.

[0124] In some embodiments, the TRP transmits, to the UE, an indication of the PRACH preamble to be transmitted by the UE to the URP and RACH resources for transmission of the PRACH preamble to the URP. Such embodiments are particular advantageous when the TRP instructs the UE to form a wireless communications link with the URP because the TRP can inform the URP which RACH resources to monitor for the PRACH preamble from the UE. In some embodiments, the RACH resources and PRACH preamble are indicated to the UE in the form of a PDDCH order. This indication may be comprised in the assistance signal or transmitted as a separate signal.

[0125] In some embodiments, the UE transmits the PRACH preamble to the URP using an omnidirectional antenna. In such embodiments, the response to the synchronisation signal transmitted from the TRP to the UE may be a random access response (RAR).

[0126] In some embodiments, the UE transmits the PRACH preamble to the URP using beam sweeping where the PRACH preamble is transmitted in different directions in different times.

[0127] In some embodiments, the assistance signal comprises an indication of an uplink beam for the UE to use in transmitting the PRACH preamble to the URP. This indication may be comprised in the assistance signal or transmitted as a separate signal. Such embodiments are particularly advantageous when the TRP instructs the UE to form a wireless communications link with the URP because the TRP is aware of the location of the UE and the URP, and can therefore determine suitable uplink beam for the UE to use for transmitting the PRACH preamble (for example, the TRP may select the uplink beam which is most closely aligned with the UE and the URP). In some embodiments, the indication of the uplink beam is indicated to the UE in the form of a PDCCH order.

[0128] In some embodiments, the TRP transmits downlink control information (DCI) to the UE comprising an indication of communications resources which the TRP will use to transmit the RAR. For example, the DCI may indicate scheduling of a physical downlink control channel (PDSCH) which carries the RAR. The RAR may comprise an indication of the propagation delay between the UE and the URP. For example, the RAR may comprise the TA between the UE and the URP. The UE may then apply the TA to uplink transmissions to the URP. In some embodiments, the assistance signal may comprise the DCI, or the DCI is transmitted as a separate signal.

[0129] In some embodiments, the RAR transmitted by the TRP in response to the UE transmitting the PRACH preamble to the URP is distinguishable from RARs transmitted from the TRP to the UE in response to PRACH preambles transmitted from the UE to the TRP. For example, they may be distinguishable by different CORESET carrying RAR DCI, different Typel- PDCCH common search space where PDCCH carries RAR DCI, different RA-RNTI for RAR DCI, explicit indication by a field of RAR DCI, or explicit indication by RAR content.

[0130] Sounding Reference Signal (SRS) In some embodiments, as mentioned above, the synchronisation signal is an SRS.

[0131] In some embodiments, the UE periodically or aperiodically transmits an SRS to the URP. In some embodiments, the assistance signal may be transmitted in DCI, or as a PDCCH order, and triggers the UE to transmit the SRS to the URP.

[0132] Uplink Transmissions to the URP

[0133] In some embodiments, uplink transmissions from the UE to the URP are each associated with a virtual SSB index or CSI-index (virtual in the sense they are associated with the URP but not transmitted by the URP). The virtual SSB indexes or CSI-indexes are transmitted from the TRP to the UE, for example, via RRC. The virtual SSB indexes or CSI indexes may be used for determining a TCI state (i.e. , uplink beam) of each of the respective uplink transmissions to the URP, which defines a Quasi-Co-Location (QCL) assumption for each respective uplink transmission.

[0134] In some embodiments, where the URP has the same SSB index as the TRP, uplink transmissions from the UE to the URP are associated with new IDs to distinguish between uplink transmissions for the TRP and uplink transmissions for the URP. The new ID may be used by the URP to determine a TCI of each respective uplink transmission (instead of using SSB indexes or CSI-RS indexes). The new IDs may be indicated to the UE by the TRP via SIB or RRC, for example. The new IDs may, for example, add an offset to a beam index of the TRP. In some embodiments, to distinguish between uplink transmissions to the TRP and the URP, where the TRP and the URP operate using the same carrier frequency, the uplink transmissions to the URP may be scrambled, or initialized, with their respective new ID.

[0135] Further examples of feature combinations taught by the present disclosure are set out in the following numbered paragraphs:

[0136] Paragraph 1 . A method of operating a communications device, the method comprising receiving, from a transmission and reception point, TRP, of a heterogeneous communications network, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device, and the method comprises determining, based on the assistance signal, to form the wireless communications link with the URP, and forming the wireless communications link with the URP, the forming the wireless communications link with the URP comprising transmitting a synchronisation signal to the URP. Paragraph 2. A method according to paragraph 1 , wherein the assistance signal comprises an indication of a downlink received reference power, RSRP, threshold, and the determining to form the wireless communications link with the URP comprises determining that an RSRP of a downlink signal received by the communications device from the TRP is below the downlink RSRP threshold.

[0137] Paragraph 3. A method according to paragraph 1 or paragraph 2, wherein the assistance signal comprises an indication of a pathloss threshold, and the determining to form the wireless communications link with the URP comprises determining that a pathloss of a downlink signal received by the communications device from the TRP is above the pathloss threshold.

[0138] Paragraph 4. A method according to any of paragraphs 1 to 3, wherein the assistance signal comprises one or more of an uplink bandwidth part or random-access resources for transmission of the synchronisation signal to the URP.

[0139] Paragraph 5. A method according to paragraph 1 , wherein the assistance signal comprises an instruction for the communications device to form the wireless communications link with the URP, and the determining to form the wireless communications link with the URP comprises identifying that the assistance signal comprises an instruction for the communications device to form the wireless communications link with the URP.

[0140] Paragraph 6. A method according to paragraph 5, comprising receiving a downlink signal from the TRP, measuring a reference signal received power, RSRP, of the downlink signal, transmitting an indication of the RSRP of the downlink signal to the TRP.

[0141] Paragraph 7. A method according to any of paragraphs 5 or 6, comprising transmitting, to the TRP, an indication of the location of the communications device in the cell provided by the TRP.

[0142] Paragraph 8. A method according to any of paragraphs 5 to 7, wherein the instruction in the assistance signal comprises a Physical Downlink Control Channel, PDCCH, order comprising an identification of the synchronisation signal to transmit to the URP.

[0143] Paragraph 9. A method according to any of paragraphs 1 to 8, wherein the method comprises determining that the communications device has not received a response to the synchronisation signal within a pre-defined time interval, and in response, and retransmitting the synchronisation signal to the URP.

[0144] Paragraph 10. A method according to paragraph 9, wherein the determining that the communications device has not received a response within a pre-defined time interval and the transmitting the synchronisation signal to the URP are repeated periodically. Paragraph 11 . A method according to any of paragraphs 1 to 10, wherein the assistance signal is comprised in a system information block, SIB.

[0145] Paragraph 12. A method according to any of paragraphs 1 to 11 , wherein the assistance signal is comprised in a Radio Resource Control, RRC, signal.

[0146] Paragraph 13. A method according to paragraph 12, wherein the RRC signal is dedicated for the communications device.

[0147] Paragraph 14. A method according to any of paragraphs 1 to 13, wherein the forming of the wireless communications link with the URP comprises receiving, from the TRP, a response to the synchronisation signal comprising an indication of a propagation delay (tP2) between the URP and the communications device, using the indication of the propagation delay to synchronise a transmission time of each of the one or more uplink transmissions at the communications device with a reception time of each of the one or more uplink transmissions at the URP.

[0148] Paragraph 15. A method according to paragraph 14, comprising receiving downlink control information from the TRP indicating that the response to the synchronisation signal is in respect of the synchronisation signal transmitted to the URP.

[0149] Paragraph 16. A method according to any of paragraphs 1 to 15, wherein the synchronisation signal is a physical random access channel, PRACH, preamble.

[0150] Paragraph 17. A method according to paragraph 16, wherein the communications device transmits the PRACH preamble towards the URP using an omni-directional antenna.

[0151] Paragraph 18. A method according to paragraph 16 wherein the communications device transmits the PRACH preamble to the URP using beam sweeping.

[0152] Paragraph 19. A method according to any of paragraphs 1 to 15, wherein the synchronisation signal is a sounding reference signal, SRS.

[0153] Paragraph 20. A method according to any of paragraphs 1 to 19, wherein the communications device transmits the synchronisation signal using pre-configured transmission gaps.

[0154] Paragraph 21. A method according to any of paragraphs 1 to 20, comprising receiving, from the TRP, a synchronisation signal block, SSB, index or Channel State Information Reference Signal (CSI-RS) index for an uplink transmission to the URP, and using the SSB index or CSI-RS index to determine a transmission configuration indicator (TCI) state for the uplink transmission.

[0155] Paragraph 22. A method of operating a transmission and reception point, TRP, of a heterogeneous communications network, the method comprising transmitting, to a communications device, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0156] Paragraph 23. A method according to paragraph 22, wherein the method comprises receiving, from the URP, a synchronisation signal transmitted to the URP by the communications device, receiving, from the URP, an indication of a propagation delay (tpi+tP2) between the TRP and the URP via the communications device, transmitting, to the communications device, a response to the synchronisation signal, the response comprising an indication of a propagation delay (tP2) between the URP and the communications device determined by the TRP based on a propagation delay (tpi+tP2) between the TRP and URP via the communications device, and based on a propagation delay (tpi) between the TRP and the communications device.

[0157] Paragraph 24. A method according to paragraph 23, wherein the TRP determines the propagation delay (tP2) between the communications device and the URP using the following equation: tp2= (tpi+tp2) - (2*tpi) / 2

[0158] Paragraph 25. A method according to any of paragraphs 22 to 24, wherein the indication of the propagation delay is a timing advance for the communications device to apply to uplink transmissions to the URP, the timing advance being twice the propagation delay (tP2) between the URP and the communications device.

[0159] Paragraph 26. A method of operating an uplink-only reception point, URP, of a heterogeneous communications network, the method comprising receiving, from a transmission and reception point, TRP, of the heterogeneous communications network, an indication of communications resources in which a synchronisation signal is to be transmitted from a communications device to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, monitoring the indicated communications resources for the synchronisation signal, and if the URP receives the synchronisation signal in the indicated communications resources, transmitting an indication to the TRP that the uplink synchronisation signal has been received, or if the URP does not receive the synchronisation signal in the indicated communications resources, transmitting an indication to the TRP that the uplink synchronisation signal has not been received, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0160] Paragraph 27. A method according to paragraph 26, wherein the transmitting the indication that the synchronisation signal has been received comprises transmitting the synchronisation signal to the TRP.

[0161] Paragraph 28. A method of operating a communications device, the method comprising determining to form a wireless communications link with an uplink-only reception point, URP, of a heterogeneous communications network for transmitting uplink transmissions to the URP, and forming the wireless communications link with the URP, wherein the forming the wireless communications link comprises transmitting a synchronisation signal to the URP, receiving, from a transmission and reception point, TRP, of the heterogeneous communications network a response to the synchronisation signal comprising an indication of a propagation delay (tP2) between the URP and the communications device, and using the indication of the propagation delay (tP2) to synchronise a transmission time of each of the one or more uplink transmissions at the communications device with a reception time of each of the one or more uplink transmissions at the URP, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0162] Paragraph 29. A method of operating a transmission and reception point, TRP, of a heterogeneous communications network, the method comprising receiving, from an uplink-only reception point, URP, of the heterogeneous communications network URP, a synchronisation signal transmitted to the URP by the communications device, receiving, from the URP, an indication of a propagation delay (tpi+ tP2) between the TRP and the URP via the communications device, transmitting, to the communications device, a response to the synchronisation signal, the response comprising an indication of a propagation delay (tP2) between the URP and the communications device determined by the TRP based on the propagation delay (tpi+ tP2) between the TRP and URP via the communications device, and based on a propagation delay (tP2) between the TRP and the communications device, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0163] Paragraph 30. A method of operating an uplink-only reception point, URP, of a heterogeneous communications network, the method comprising receiving a synchronisation signal from a communications device, transmitting the synchronisation signal to a transmission and reception point, TRP, of the heterogeneous communications network, transmitting, to the TRP, an indication of a propagation delay (tpi+ tP2) between the TRP and URP via the communications device, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0164] Paragraph 31. A communications device, the communications device comprising a transmitter configured to transmit signals, a receiver configured to receive signals, and a controller configured in combination with the transmitter and the receiver to receive, from a transmission and reception point, TRP, of a heterogeneous communications network, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device, and the controller is configured in combination with the transmitter and the receiver to determine, based on the assistance signal, to form the wireless communications link with the URP, and form the wireless communications link with the URP, the forming the wireless communications link with the URP comprising transmitting a synchronisation signal to the URP.

[0165] Paragraph 32. Circuitry for a communications device, the circuitry comprising transmitter circuitry configured to transmit signals, receiver circuitry configured to receive signals, and controller circuitry configured in combination with the transmitter circuitry and the receiver circuitry to receive, from a transmission and reception point, TRP, of a heterogeneous communications network, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device, and the controller circuitry is configured in combination with the transmitter circuitry and the receiver circuitry to determine, based on the assistance signal, to form the wireless communications link with the URP, and form the wireless communications link with the URP, the forming the wireless communications link with the URP comprising transmitting a synchronisation signal to the URP.

[0166] Paragraph 33. A transmission and reception point, TRP, for a heterogeneous communications network, the TRP comprising a transmitter configured to transmit signals, a receiver configured to receive signals, and a controller configured in combination with the transmitter and the receiver to transmit, to a communications device, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0167] Paragraph 34. Circuitry for a transmission and reception point, TRP, for a heterogeneous communications network, the circuitry comprising transmitter circuitry configured to transmit signals, receiver circuitry configured to receive signals, and controller circuitry configured in combination with the transmitter circuitry and the receiver circuitry to transmit, to a communications device, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0168] Paragraph 35. An uplink-only reception point, URP, for a heterogeneous communications network, the URP comprising a transmitter configured to transmit signals, a receiver configured to receive signals, and a controller configured in combination with the transmitter and the receiver to receive, from a transmission and reception point, TRP, of the heterogeneous communications network, an indication of communications resources in which a synchronisation signal is to be transmitted from a communications device to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, monitor the indicated communications resources for the synchronisation signal, and if the URP receives the synchronisation signal in the indicated communications resources, transmit an indication to the TRP that the uplink synchronisation signal has been received, or if the URP does not receive the synchronisation signal in the indicated communications resources, transmit an indication to the TRP that the uplink synchronisation signal has not been received, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0169] Paragraph 36. Circuitry for an uplink-only reception point, URP, for a heterogeneous communications network, the circuitry comprising transmitter circuitry configured to transmit signals, receiver circuitry configured to receive signals, and controller circuitry configured in combination with the transmitter circuitry and the receiver circuitry to receive, from a transmission and reception point, TRP, of the heterogeneous communications network, an indication of communications resources in which a synchronisation signal is to be transmitted from a communications device to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, monitor the indicated communications resources for the synchronisation signal, and if the URP receives the synchronisation signal in the indicated communications resources, transmit an indication to the TRP that the uplink synchronisation signal has been received, or if the URP does not receive the synchronisation signal in the indicated communications resources, transmit an indication to the TRP that the uplink synchronisation signal has not been received, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0170] Paragraph 37. A communications device, the communications device comprising a transmitter configured to transmit signals, a receiver configured to receive signals, and a controller configured in combination with the transmitter and the receiver to determine to form a wireless communications link with an uplink-only reception point, URP, of a heterogeneous communications network for transmitting uplink transmissions to the URP, and form the wireless communications link with the URP, wherein the forming the wireless communications link comprises transmitting a synchronisation signal to the URP, receiving, from a transmission and reception point, TRP, of the heterogeneous communications network a response to the synchronisation signal comprising an indication of a propagation delay (tP2) between the URP and the communications device, and using the indication of the propagation delay (tP2) to synchronise a transmission time of each of the one or more uplink transmissions at the communications device with a reception time of each of the one or more uplink transmissions at the URP, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0171] Paragraph 38. Circuitry for a communications device, the circuitry comprising transmitter circuitry configured to transmit signals, receiver circuitry configured to receive signals, and controller circuitry configured in combination with the transmitter circuitry and the receiver circuitry to determine to form a wireless communications link with an uplink-only reception point, URP, of a heterogeneous communications network for transmitting uplink transmissions to the URP, and form the wireless communications link with the URP, wherein the forming the wireless communications link comprises transmitting a synchronisation signal to the URP, receiving, from a transmission and reception point, TRP, of the heterogeneous communications network a response to the synchronisation signal comprising an indication of a propagation delay (tP2) between the URP and the communications device, and using the indication of the propagation delay (tP2) to synchronise a transmission time of each of the one or more uplink transmissions at the communications device with a reception time of each of the one or more uplink transmissions at the URP, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0172] Paragraph 39. A transmission and reception point, TRP, for a heterogeneous communications network, the TRP comprising a transmitter configured to transmit signals, a receiver configured to receive signals, and a controller configured in combination with the transmitter and the receiver to receive, from an uplink-only reception point, URP, of the heterogeneous communications network URP, a synchronisation signal transmitted to the URP by the communications device, receive, from the URP, an indication of a propagation delay (tpi+ tP2) between the TRP and the URP via the communications device, transmit, to the communications device, a response to the synchronisation signal, the response comprising an indication of a propagation delay (tP2) between the URP and the communications device determined by the TRP based on the propagation delay (tpi+ tP2) between the TRP and URP via the communications device, and based on a propagation delay (tP2) between the TRP and the communications device, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0173] Paragraph 40. Circuitry for a transmission and reception point, TRP, for a heterogeneous communications network, the circuitry comprising transmitter circuitry configured to transmit signals, receiver circuitry configured to receive signals, and controller circuitry configured in combination with the transmitter circuitry and the receiver circuitry to receive, from an uplink-only reception point, URP, of the heterogeneous communications network URP, a synchronisation signal transmitted to the URP by the communications device, receive, from the URP, an indication of a propagation delay (tpi+ tP2) between the TRP and the URP via the communications device, transmit, to the communications device, a response to the synchronisation signal, the response comprising an indication of a propagation delay (tP2) between the URP and the communications device determined by the TRP based on the propagation delay (tpi+ tP2) between the TRP and URP via the communications device, and based on a propagation delay (tP2) between the TRP and the communications device, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0174] Paragraph 41 . An uplink-only reception point, URP, for a heterogeneous communications network, the URP comprising a transmitter configured to transmit signals, a receiver configured to receive signals, and a controller configured in combination with the transmitter and the receiver to receive a synchronisation signal from a communications device, transmit the synchronisation signal to a transmission and reception point, TRP, of the heterogeneous communications network, transmit, to the TRP, an indication of a propagation delay (tpi+ tP2) between the TRP and URP via the communications device, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0175] Paragraph 42. Circuitry for an uplink-only reception point, URP, for a heterogeneous communications network, the circuitry comprising transmitter circuitry configured to transmit signals, receiver circuitry configured to receive signals, and controller circuitry configured in combination with the transmitter circuitry and the receiver circuitry to receive a synchronisation signal from a communications device, transmit the synchronisation signal to a transmission and reception point, TRP, of the heterogeneous communications network, transmit, to the TRP, an indication of a propagation delay (tpi+ tP2) between the TRP and URP via the communications device, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

[0176] Paragraph 43. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to perform the method of any of paragraphs 1 to 30.

[0177] Paragraph 44. A non-transitory computer-readable storage medium storing a computer program according to paragraph 43.

[0178] REFERENCES

[0179] [1] Holma H. and Toskala A, “LTE for UMTS OFDMA and SC-FDMA based radio access”, John Wiley and Sons, 2009.

[0180] [2] RWS-230248, “Views on Rel-19 MIMO / UL enhancements,” NTT DOCOMO, 3GPP TSG RAN Rel-19 workshop.

[0181] [3] TS 38.211, ’’Physical channels and modulation (Release 17)”, v17.3.0, 3GPP.

Claims

CLAIMS1 . A method of operating a communications device, the method comprising receiving, from a transmission and reception point, TRP, of a heterogeneous communications network, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device, and the method comprises determining, based on the assistance signal, to form the wireless communications link with the URP, and forming the wireless communications link with the URP, the forming the wireless communications link with the URP comprising transmitting a synchronisation signal to the URP.

2. A method according to claim 1 , wherein the assistance signal comprises an indication of a downlink received reference power, RSRP, threshold, and the determining to form the wireless communications link with the URP comprises determining that an RSRP of a downlink signal received by the communications device from the TRP is below the downlink RSRP threshold.

3. A method according to claim 1 , wherein the assistance signal comprises an indication of a pathloss threshold, and the determining to form the wireless communications link with the URP comprises determining that a pathloss of a downlink signal received by the communications device from the TRP is above the pathloss threshold.

4. A method according to claim 1 , wherein the assistance signal comprises one or more of an uplink bandwidth part or random-access resources for transmission of the synchronisation signal to the URP.

5. A method according to claim 1 , wherein the assistance signal comprises an instruction for the communications device to form the wireless communications link with the URP, and the determining to form the wireless communications link with the URP comprises identifying that the assistance signal comprises an instruction for the communications device to form the wireless communications link with the URP.

6. A method according to claim 5, comprising receiving a downlink signal from the TRP, measuring a reference signal received power, RSRP, of the downlink signal, transmitting an indication of the RSRP of the downlink signal to the TRP.

7. A method according to claim 5, comprising transmitting, to the TRP, an indication of the location of the communications device in the cell provided by the TRP.

8. A method according to claim 5, wherein the instruction in the assistance signal comprises a Physical Downlink Control Channel, PDCCH, order comprising an identification of the synchronisation signal to transmit to the URP.

9. A method according to claim 1 , wherein the method comprises determining that the communications device has not received a response to the synchronisation signal within a pre-defined time interval, and in response, and retransmitting the synchronisation signal to the URP.

10. A method according to claim 9, wherein the determining that the communications device has not received a response within a pre-defined time interval and the transmitting the synchronisation signal to the URP are repeated periodically.

11. A method according to claim 1 , wherein the assistance signal is comprised in a system information block, SIB.

12. A method according to claim 1, wherein the assistance signal is comprised in a Radio Resource Control, RRC, signal.

13. A method according to claim 12, wherein the RRC signal is dedicated for the communications device.

14. A method according to claim 1 , wherein the forming of the wireless communications link with the URP comprises receiving, from the TRP, a response to the synchronisation signal comprising an indication of a propagation delay (tP2) between the URP and the communications device, using the indication of the propagation delay to synchronise a transmission time of each of the one or more uplink transmissions at the communications device with a reception time of each of the one or more uplink transmissions at the URP.

15. A method according to claim 14, comprising receiving downlink control information from the TRP indicating that the response to the synchronisation signal is in respect of the synchronisation signal transmitted to the URP.

16. A method according to claim 1 , wherein the synchronisation signal is a physical random access channel, PRACH, preamble.

17. A method according to claim 16, wherein the communications device transmits the PRACH preamble towards the URP using an omni-directional antenna.

18. A method according to claim 16 wherein the communications device transmits the PRACH preamble to the URP using beam sweeping.

19. A method according to claim 1 , wherein the synchronisation signal is a sounding reference signal, SRS.

20. A method according to claim 1 , wherein the communications device transmits the synchronisation signal using pre-configured transmission gaps.21 . A method according to claim 1 , comprising receiving, from the TRP, a synchronisation signal block, SSB, index or Channel State Information Reference Signal (CSI-RS) index for an uplink transmission to the URP, and using the SSB index or CSI-RS index to determine a transmission configuration indicator (TCI) state for the uplink transmission.

22. A method of operating a transmission and reception point, TRP, of a heterogeneous communications network, the method comprising transmitting, to a communications device, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

23. A method according to claim 22, wherein the method comprises receiving, from the URP, a synchronisation signal transmitted to the URP by the communications device, receiving, from the URP, an indication of a propagation delay (tpi+tP2) between the TRP and the URP via the communications device, transmitting, to the communications device, a response to the synchronisation signal, the response comprising an indication of a propagation delay (tP2) between the URP and the communications device determined by the TRP based on a propagation delay (tpi+tP2) between the TRP and URP via the communications device, and based on a propagation delay (tpi) between the TRP and the communications device.

24. A method according to claim 23, wherein the TRP determines the propagation delay (tP2) between the communications device and the URP using the following equation: tP2 = (tpi+tP2) - (2*tpi) / 225. A method according to claim 22, wherein the indication of the propagation delay is a timing advance for the communications device to apply to uplink transmissions to the URP, the timing advance being twice the propagation delay (tP2) between the URP and the communications device.

26. A method of operating an uplink-only reception point, URP, of a heterogeneous communications network, the method comprising receiving, from a transmission and reception point, TRP, of the heterogeneous communications network, an indication of communications resources in which a synchronisation signal is to be transmitted from a communications device to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link,monitoring the indicated communications resources for the synchronisation signal, and if the URP receives the synchronisation signal in the indicated communications resources, transmitting an indication to the TRP that the uplink synchronisation signal has been received, or if the URP does not receive the synchronisation signal in the indicated communications resources, transmitting an indication to the TRP that the uplink synchronisation signal has not been received, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

27. A method according to claim 26, wherein the transmitting the indication that the synchronisation signal has been received comprises transmitting the synchronisation signal to the TRP.

28. A method of operating a communications device, the method comprising determining to form a wireless communications link with an uplink-only reception point, URP, of a heterogeneous communications network for transmitting uplink transmissions to the URP, and forming the wireless communications link with the URP, wherein the forming the wireless communications link comprises transmitting a synchronisation signal to the URP, receiving, from a transmission and reception point, TRP, of the heterogeneous communications network a response to the synchronisation signal comprising an indication of a propagation delay (tP2) between the URP and the communications device, and using the indication of the propagation delay (tP2) to synchronise a transmission time of each of the one or more uplink transmissions at the communications device with a reception time of each of the one or more uplink transmissions at the URP, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

29. A method of operating a transmission and reception point, TRP, of a heterogeneous communications network, the method comprisingreceiving, from an uplink-only reception point, URP, of the heterogeneous communications network URP, a synchronisation signal transmitted to the URP by the communications device, receiving, from the URP, an indication of a propagation delay (tpi+ tP2) between the TRP and the URP via the communications device, transmitting, to the communications device, a response to the synchronisation signal, the response comprising an indication of a propagation delay (tP2) between the URP and the communications device determined by the TRP based on the propagation delay (tpi+ tP2) between the TRP and URP via the communications device, and based on a propagation delay (tP2) between the TRP and the communications device, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

30. A method of operating an uplink-only reception point, URP, of a heterogeneous communications network, the method comprising receiving a synchronisation signal from a communications device, transmitting the synchronisation signal to a transmission and reception point, TRP, of the heterogeneous communications network, transmitting, to the TRP, an indication of a propagation delay (tpi+ tP2) between the TRP and URP via the communications device, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.31 . A communications device, the communications device comprising a transmitter configured to transmit signals, a receiver configured to receive signals, and a controller configured in combination with the transmitter and the receiver to receive, from a transmission and reception point, TRP, of a heterogeneous communications network, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, whereinthe TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device, and the controller is configured in combination with the transmitter and the receiver to determine, based on the assistance signal, to form the wireless communications link with the URP, and form the wireless communications link with the URP, the forming the wireless communications link with the URP comprising transmitting a synchronisation signal to the URP.

32. Circuitry for a communications device, the circuitry comprising transmitter circuitry configured to transmit signals, receiver circuitry configured to receive signals, and controller circuitry configured in combination with the transmitter circuitry and the receiver circuitry to receive, from a transmission and reception point, TRP, of a heterogeneous communications network, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device, and the controller circuitry is configured in combination with the transmitter circuitry and the receiver circuitry to determine, based on the assistance signal, to form the wireless communications link with the URP, and form the wireless communications link with the URP, the forming the wireless communications link with the URP comprising transmitting a synchronisation signal to the URP.

33. A transmission and reception point, TRP, for a heterogeneous communications network, the TRP comprising a transmitter configured to transmit signals,a receiver configured to receive signals, and a controller configured in combination with the transmitter and the receiver to transmit, to a communications device, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

34. Circuitry for a transmission and reception point, TRP, for a heterogeneous communications network, the circuitry comprising transmitter circuitry configured to transmit signals, receiver circuitry configured to receive signals, and controller circuitry configured in combination with the transmitter circuitry and the receiver circuitry to transmit, to a communications device, an assistance signal comprising information for the communications device to determine whether to form a wireless communications link with an uplink-only reception point, URP, of the heterogeneous communications network for transmitting uplink transmissions to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

35. An uplink-only reception point, URP, for a heterogeneous communications network, the URP comprising a transmitter configured to transmit signals, a receiver configured to receive signals, and a controller configured in combination with the transmitter and the receiver to receive, from a transmission and reception point, TRP, of the heterogeneous communications network, an indication of communications resources in which a synchronisation signal is to be transmitted from a communications device to the URP, the URPbeing configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, monitor the indicated communications resources for the synchronisation signal, and if the URP receives the synchronisation signal in the indicated communications resources, transmit an indication to the TRP that the uplink synchronisation signal has been received, or if the URP does not receive the synchronisation signal in the indicated communications resources, transmit an indication to the TRP that the uplink synchronisation signal has not been received, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

36. Circuitry for an uplink-only reception point, URP, for a heterogeneous communications network, the circuitry comprising transmitter circuitry configured to transmit signals, receiver circuitry configured to receive signals, and controller circuitry configured in combination with the transmitter circuitry and the receiver circuitry to receive, from a transmission and reception point, TRP, of the heterogeneous communications network, an indication of communications resources in which a synchronisation signal is to be transmitted from a communications device to the URP, the URP being configured to transmit signals to, and receive signals from, the TRP via a backhaul communications link, monitor the indicated communications resources for the synchronisation signal, and if the URP receives the synchronisation signal in the indicated communications resources, transmit an indication to the TRP that the uplink synchronisation signal has been received, or if the URP does not receive the synchronisation signal in the indicated communications resources, transmit an indication to the TRP that the uplink synchronisation signal has not been received, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

37. A communications device, the communications device comprising a transmitter configured to transmit signals, a receiver configured to receive signals, and a controller configured in combination with the transmitter and the receiver to determine to form a wireless communications link with an uplink-only reception point, URP, of a heterogeneous communications network for transmitting uplink transmissions to the URP, and form the wireless communications link with the URP, wherein the forming the wireless communications link comprises transmitting a synchronisation signal to the URP, receiving, from a transmission and reception point, TRP, of the heterogeneous communications network a response to the synchronisation signal comprising an indication of a propagation delay (tP2) between the URP and the communications device, and using the indication of the propagation delay (tP2) to synchronise a transmission time of each of the one or more uplink transmissions at the communications device with a reception time of each of the one or more uplink transmissions at the URP, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

38. Circuitry for a communications device, the circuitry comprising transmitter circuitry configured to transmit signals, receiver circuitry configured to receive signals, and controller circuitry configured in combination with the transmitter circuitry and the receiver circuitry to determine to form a wireless communications link with an uplink-only reception point, URP, of a heterogeneous communications network for transmitting uplink transmissions to the URP, and form the wireless communications link with the URP, wherein the forming the wireless communications link comprises transmitting a synchronisation signal to the URP, receiving, from a transmission and reception point, TRP, of the heterogeneous communications network a response to the synchronisation signal comprising an indication of a propagation delay (tP2) between the URP and the communications device, andusing the indication of the propagation delay (tP2) to synchronise a transmission time of each of the one or more uplink transmissions at the communications device with a reception time of each of the one or more uplink transmissions at the URP, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

39. A transmission and reception point, TRP, for a heterogeneous communications network, the TRP comprising a transmitter configured to transmit signals, a receiver configured to receive signals, and a controller configured in combination with the transmitter and the receiver to receive, from an uplink-only reception point, URP, of the heterogeneous communications network URP, a synchronisation signal transmitted to the URP by the communications device, receive, from the URP, an indication of a propagation delay (tpi+ tP2) between the TRP and the URP via the communications device, transmit, to the communications device, a response to the synchronisation signal, the response comprising an indication of a propagation delay (tP2) between the URP and the communications device determined by the TRP based on the propagation delay (tpi+ tP2) between the TRP and URP via the communications device, and based on a propagation delay (tP2) between the TRP and the communications device, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

40. Circuitry for a transmission and reception point, TRP, for a heterogeneous communications network, the circuitry comprising transmitter circuitry configured to transmit signals, receiver circuitry configured to receive signals, and controller circuitry configured in combination with the transmitter circuitry and the receiver circuitry toreceive, from an uplink-only reception point, URP, of the heterogeneous communications network URP, a synchronisation signal transmitted to the URP by the communications device, receive, from the URP, an indication of a propagation delay (tpi+ tP2) between the TRP and the URP via the communications device, transmit, to the communications device, a response to the synchronisation signal, the response comprising an indication of a propagation delay (tP2) between the URP and the communications device determined by the TRP based on the propagation delay (tpi+ tP2) between the TRP and URP via the communications device, and based on a propagation delay (tP2) between the TRP and the communications device, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

41. An uplink-only reception point, URP, for a heterogeneous communications network, the URP comprising a transmitter configured to transmit signals, a receiver configured to receive signals, and a controller configured in combination with the transmitter and the receiver to receive a synchronisation signal from a communications device, transmit the synchronisation signal to a transmission and reception point, TRP, of the heterogeneous communications network, transmit, to the TRP, an indication of a propagation delay (tpi+ tP2) between the TRP and URP via the communications device, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

42. Circuitry for an uplink-only reception point, URP, for a heterogeneous communications network, the circuitry comprising transmitter circuitry configured to transmit signals, receiver circuitry configured to receive signals, and controller circuitry configured in combination with the transmitter circuitry and the receiver circuitry toreceive a synchronisation signal from a communications device, transmit the synchronisation signal to a transmission and reception point, TRP, of the heterogeneous communications network, transmit, to the TRP, an indication of a propagation delay (tpi+ tP2) between the TRP and URP via the communications device, wherein the TRP provides a cell for the communications device to transmit uplink transmissions to, and receive downlink transmissions from, the TRP when the communications device is located within the cell provided by the TRP, and the URP provides an uplink-only cell for the communications device to transmit uplink transmissions to the URP when the communications device is located within the uplink-only cell, the URP being unable to transmit downlink transmissions to the communications device.

43. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to perform the method of claim 1.

44. A non-transitory computer-readable storage medium storing a computer program according to claim 43.

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