Methods, communications devices, and infrastructure equipment

Abstract

A method of operating a communications device to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment is provided. The method comprises while a low-power receiver of the communications device is in an ON state, receiving, by the low-power receiver, one or more synchronisation signals (SSs) from the infrastructure equipment in one or more predefined SS reception periods. The method comprises, while the low power receiver is in the ON state, synchronising the low-power receiver with the infrastructure equipment based on the one or more received SSs. The method comprises, while the low power receiver is in the ON state, monitoring, with the synchronised low-power receiver, one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment. If the synchronised low-power receiver receives a WUS in one of the WUS monitoring periods, the method comprises while a main receiver of the communications device is in the ON state, monitoring, with the main receiver, a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment. The downlink signal monitoring period is subsequent to the WUS monitoring period in which the WUS was received. A power consumption of the low-power receiver when the low-power receiver is in the ON state is lower than a power consumption of the main receiver when the main receiver is in the ON state.

Description

[0001] METHODS, COMMUNICATIONS DEVICES, AND INFRASTRUCTURE EQUIPMENT

[0002] BACKGROUND

[0003] Field of Disclosure

[0004] The present disclosure relates to communications devices, infrastructure equipment and methods for the more effective power saving of communications devices in wireless communications networks.

[0005] The present disclosure claims Paris Convention priority from EP patent application number 24153273.8, filed on 22 January 2024, 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] Previous generation 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] Current and future wireless communications networks are expected to routinely and efficiently support communications with an ever-increasing range of devices associated with a wider range of data traffic profiles and types than existing systems are optimised to support. For example, it is expected future wireless communications networks will be expected to efficiently support communications with devices including reduced complexity devices, machine type communication (MTC) devices, high resolution video displays, virtual reality headsets, extended Reality (XR) 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 expected to be a desire for current wireless communications networks, for example those which may be referred to as 5G or new radio (NR) systems I new radio access technology (RAT) systems, or indeed future 6G wireless communications, 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] One example of a new service is referred to as Ultra Reliable Low Latency Communications (URLLC) services which, as its name suggests, requires that a data unit or packet be communicated with a high reliability and with a low communications delay. Another example of a new service is enhanced Mobile Broadband (eMBB) services, which are characterised by a high capacity with a requirement to support up to 20 Gb / s. URLLC and eMBB type services therefore represent challenging examples for both LTE type communications systems and 5G / NR communications systems.

[0011] 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.

[0012] SUMMARY OF THE DISCLOSURE

[0013] The present disclosure can help address or mitigate at least some of the issues discussed above.

[0014] Example embodiments can provide, in a first aspect, a method of operating a communications device to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment. The method comprises while a low-power receiver of the communications device is in an ON state, receiving, by the low-power receiver, one or more synchronisation signals (SSs) from the infrastructure equipment in one or more predefined SS reception periods. The method comprises, while the low power receiver is in the ON state, synchronising the low-power receiver with the infrastructure equipment based on the one or more received SSs. The method comprises, while the low power receiver is in the ON state, monitoring, with the synchronised low-power receiver, one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment. If the synchronised low-power receiver receives a WUS in one of the WUS monitoring periods, the method comprises while a main receiver of the communications device is in the ON state, monitoring, with the main receiver, a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment. The downlink signal monitoring period is subsequent to the WUS monitoring period in which the WUS was received. A power consumption of the low-power receiver when the low-power receiver is in the ON state is lower than a power consumption of the main receiver when the main receiver is in the ON state.

[0015] Example embodiments can provide, in a second aspect, a method of operating a communications device to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment. The method comprises while a low-power receiver of the communications device is in an ON state, monitoring, with a low-power receiver of the communications device, one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment. If the low-power receiver receives a WUS in one of the WUS monitoring periods, the method comprises while a main receiver of the communications device is in the ON state, monitoring, with the main receiver, a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment. The downlink signal monitoring period is subsequent to the WUS monitoring period in which the WUS was received. A power consumption of the low-power receiver when the low-power receiver is in the ON state is lower than a power consumption of the main receiver when the main receiver is in the ON state. The received WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface. A first of the OFDM symbols is an identification symbol and the OFDM symbols subsequent to the identification symbol are data-carrying symbols. The data-carrying symbols are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence.

[0016] Example embodiments can provide, in a third aspect, a method of operating infrastructure equipment of a wireless communications network to communicate with one or more communications devices via a wireless radio interface provided by the infrastructure equipment. The method comprises transmitting a Wake-Up signal (WUS) to at least one of the communications devices in a WUS transmission period. The WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface. A first of the OFDM symbols is an identification symbol, and the OFDM symbols of the WUS subsequent to the identification symbol are data-carrying symbols. The OFDM symbols in the WUS are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence. The method comprises transmitting a downlink signal to the at least one communications device to which the WUS was transmitted in a downlink signal transmission period subsequent to the WUS transmission period.

[0017] Other Respective aspects and features of the present disclosure are defined in the appended claims.

[0018] 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.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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:

[0021] 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;

[0022] Figure 2 schematically represents some aspects of a new radio access technology (NR) wireless telecommunications system which may be configured to operate in accordance with certain embodiments of the present disclosure;

[0023] 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;

[0024] Figure 4 is a graphical plot of user equipment (UE) processing activity against time illustrating an example of a discontinuous reception (DRX) cycle; Figure 5 is a graphical plot of UE processing activity against time illustrating an example of a paging occasion preceded by a wake-up signal according to that used for LTE;

[0025] Figure 6 is a graphical plot of UE processing activity against time illustrating an example of a DRX cycle according to that used for 5G / NR;

[0026] Figure 7 schematically illustrates the relationship between a main receiver (MR) and a lower power wake-up receiver (LP-WUR) of a UE which may be configured to operate in accordance with certain embodiments of the present disclosure;

[0027] Figure 8 schematically illustrates an example of how a low-power wake-up signal (LP-WUS) may be monitored for by an LP-WUR of a UE prior to a paging occasion;

[0028] Figure 9 shows a part schematic, part message flow diagram representation of a wireless communications system comprising a communications device and an infrastructure equipment in accordance with example embodiments;

[0029] Figures 10A and 10B schematically illustrate examples of low power receiver (LPR) synchronisation in accordance with example embodiments;

[0030] Figure 11 schematically illustrates an example of an WUS OFDM symbol in the frequency domain in accordance with example embodiments;

[0031] Figure 12 is a flow diagram illustrating a method of operating a communications device in accordance with example embodiments;

[0032] Figure 13 is a flow diagram illustrating a method of operating infrastructure equipment of a wireless communications network in accordance with example embodiments.

[0033] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] Long Term Evolution Advanced Radio Access Technology (4G)

[0035] 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.

[0036] The network 6 includes a plurality of base stations 1 connected to a core network 2. Each base station provides a coverage area 3 (i.e. a cell) within which data can be communicated to and from communications devices 4. Although each base station 1 is shown in Figure 1 as a single entity, the skilled person will appreciate that some of the functions of the base station may be carried out by disparate, inter-connected elements, such as antennas (or antennae), remote radio heads, amplifiers, etc. Collectively, one or more base stations may form a radio access network. Data is transmitted from base stations 1 to communications devices 4 within their respective coverage areas 3 via a radio downlink (DL). Data is transmitted from communications devices 4 to the base stations 1 via a radio uplink (UL). 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. Communications devices may also be referred to as mobile stations, user equipment (UEs), user terminals, mobile radios, mobile terminals, terminal devices, wireless transmit and receive units (WTRUs), 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.

[0037] 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.

[0038] New Radio Access Technology (5G)

[0039] Systems incorporating NR technology are expected to support different services (or types of services), which may be characterised by different requirements for latency, data rate and / or reliability. For example, Enhanced Mobile Broadband (eMBB) services are characterised by high capacity with a requirement to support up to 20 Gb / s. The requirements for Ultra Reliable and Low Latency Communications (URLLC) services are for one transmission of a 32 byte packet to be transmitted from the radio protocol layer 2 / 3 SDU ingress point to the radio protocol layer 2 / 3 SDU egress point of the radio interface within 1 ms with a reliability of 1 - 10’5(99.999 %) or higher (99.9999%) [2],

[0040] Massive Machine Type Communications (mMTC) is another example of a service which may be supported by NR-based communications networks. In addition, systems may be expected to support further enhancements related to Industrial Internet of Things (lloT) in order to support services with new requirements of high availability, high reliability, low latency, and in some cases, high-accuracy positioning.

[0041] 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 25.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] A more detailed diagram of some of the components of the network shown in Figure 2 is provided by Figure 3. In Figure 3, a TRP 10 as shown in Figure 2 comprises, as a simplified representation, a wireless transmitter 30, a wireless receiver 32 and a controller or controlling processor 34 which may operate to control the transmitter 30 and the wireless receiver 32 to transmit and receive radio signals to one or more UEs 14 within a cell 12 formed by the TRP 10. As shown in Figure 3, an example UE 14 is shown to include a corresponding transmitter 49, a receiver 48 and a controller 44 which is configured to control the transmitter 49 and the receiver 48 to transmit signals representing uplink data to the wireless communications network via the wireless access interface formed by the TRP 10 and to receive downlink data as signals transmitted by the transmitter 30 and received by the receiver 48 in accordance with the conventional operation.

[0048] The transmitters 30, 49 and the receivers 32, 48 (as well as other transmitters, receivers and transceivers described in relation to examples and embodiments of the present disclosure) may include radio frequency filters and amplifiers as well as signal processing components and devices in order to transmit and receive radio signals in accordance for example with the 5G / NR standard. The controllers 34, 44 (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.

[0049] 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.

[0050] 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 TRP 10 to the DU 42 and the F1 interface 46 from the DU 42 to the CU 40.

[0051] In order for a UE such as UE 4 or 14 to transmit uplink data to the network (e.g. on a Physical Uplink Control Channel (PUCCH) or a Physical Uplink Shared Channel (PUSCH)) to, for example, base station 1 or TRP 10, the UE must first ensure it is synchronised with the network on the uplink. Since a particular eNB or gNB expects to be receiving communications from many UEs, it needs to ensure that it shares a common timing understanding with each of these UEs (i.e. they are synchronised in terms of the starting times of frames and Orthogonal Frequency Division Multiplexed (OFDM) symbols). This is so that the eNB is able to schedule communication with each of them in a manner that avoids collisions and to ensure orthogonality of the uplink signals, such that inter-subcarrier interference is avoided or mitigated.

[0052] Power Saving and Discontinuous Reception (DRX) in NR In a typical currently deployed network, communications devices can operate in a discontinuous reception (DRX) mode during which the communications devices wake-up (i.e. power-up their receivers) to receive signals during their DRX wake time. DRX operation can occur when the communications devices are in an idle mode or in a connected mode. In connected mode, the communications device is configured to periodically monitor physical downlink control channels (PDCCHs) in groups of slots or subframes. If a PDCCH with a Radio Network Temporary Identifier (RNTI) addressed to the communications device is not detected during the group of slots or subframes, the communications device may sleep for the next cycle of the periodicity. Power saving is an important aspect of a user’s experience of such wireless radio access technologies such as NR, which will influence the adoption of 5G and future generation handsets and / or services. DRX is one method of power saving for NR communications devices.

[0053] In legacy systems such as LTE and NR, a UE in RRC-CONNECTED mode will send a scheduling request when it has UL data to transmit. Following this, the gNB will schedule / allocate some UL transmission resources and inform the UE via DCI on PDCCH where the resources are both in time and frequency and the configuration for the UE’s UL transmission such as MCS, TBS etc. When the UE has no data to transmit in the UL, it waits in RRC-CONNECTED mode. If on the other hand data arrives at the gNB for the UE, the gNB will also schedule DL resources and inform the UE via DCI on PDCCH on the location in frequency and time of the resources and the configuration the UE is to use for DL reception on the allocated resources. Once the UE receives the DL data, it waits in RRC-CONNECTED mode for the next DL data whilst monitoring the PDCCH in every DL subframe for any scheduling information targeted at the UE. The UE battery power consumption whilst in RRC- CONNECTED mode could be quite high because of the continuous PDCCH monitoring by the UE and reception of other DL channels and signals. However, if the network knows that neither DL data for nor UL data from the UE is imminent, it is desirable that the UE goes to sleep while remaining in RRC-CONNECTED mode. In legacy LTE and NR, this entails UE undertaking RRC-CONNECTED mode DRX (C-DRX).

[0054] The basic DRX cycle is shown in Figure 4, which consists of a DRX ON period of duration TDRX-ON and a period of inactivity, i.e. a DRX OFF period, of duration TDRX-OFF where the DRX ON period occurs periodically at a DRX period, PDRX. During the DRX ON period, the UE switches on its receiver to monitor the PDCCH for downlink traffic and switches off its receiver during the DRX OFF period to save power consumption. The DRX parameters TDRX-ON & PDRX are configured by the network.

[0055] The price paid for utilising DRX operation (e.g. C-DRX) is that if data meant for a UE currently in its DRX OFF period arrives at the gNB for delivery to the UE, the gNB can only schedule the data after the DRX OFF period is finished. This latency in data scheduling that arises because of C-DRX can be reduced by initiating a timer, drx-lnactivityTimer, immediately after the UE detects a DCI scheduling data to it in one of the PDCCH it monitors during the drx- onDuration intervals of its C-DRX cycle. The effect of this timer is to increase the DRX ON time in anticipation that more data for the UE may arrive at the network. The rationale for this is that if data is being scheduled to the UE now, it is highly likely that more data to the same UE will follow.

[0056] When a UE has no data to transmit and the network has no data for the UE, the UE can transition into RRC-IDLE mode. In legacy systems, there is also RRC-IDLE mode DRX. RRC- IDLE mode DRX is set up to work in conjunction with other RRC-IDLE mode UE procedures such as paging of the UE, tracking area update (TAU) etc. Paging is used by the network to establish mobile terminated connections with the UE. During RRC-IDLE mode the UE can go to sleep to minimise battery power consumption. It is desirable however, for an RRC-IDLE mode UE to wake up regularly and listen for any paging messages that the network may have sent to initiate a mobile terminated connection with the UE or for other established reasons such as TAU. In NR, a UE can also wake up to listen to paging messages in RRC-INACTIVE mode.

[0057] For a UE that is awake, listening for a paging message entails monitoring the PDCCH during configured paging occasions for a DCI Format 1_0 whose CRC is scrambled with P-RNTI. For an RRC-IDLE mode UE with which the network is seeking to establish a mobile terminated connection, this DCI carries resource allocation information for a subsequent PDSCH that will carry the actual paging information. If the UE detects the DCI Format 1_0 scrambled with P- RNTI, the UE stays awake to receive the scheduled PDSCH; otherwise, the UE should conclude that it is not being paged and so go back to sleep. The paging information PDSCH carries such information for many targeted UEs. Therefore, the UE needs to decode the PDSCH information to decide whether any of it is meant for the said UE. This is done by determining that some of the information is targeted towards a UE with a network preconfigured UE temporary identity (5G-S-TMSI) that matches the UE’s. The cadence with which the UE wakes up to monitor for paging messages typically follows the RRC-IDLE mode DRX configuration which defines the DRX ON and OFF times in each DRX cycle. Therefore, the network is expected to initiate paging towards a given UE during its DRX ON periods.

[0058] Often, when the UE wakes up to monitor the PDCCH for a DCI Format 1_0 with CRC scrambled with P-RNTI, it would not find it. Furthermore, even when the UE does find the DCI and then goes on to decode the associated PDSCH, the UE would not find a paging message targeted towards its temporary UE identity. It is only after this that a UE which found the DCI Format 1_0 with CRC scrambled with P-RNTI can conclude that there was no page for it in this paging occasion and go back to sleep. Every time the UE wakes up and does not find a PDCCH scrambled with P-RNTI, the awake UE consumes battery power. Furthermore, every time the UE wakes up, finds a PDCCH scrambled with P-RNTI but does not find a paging message targeted towards its temporary UE identity in the PDSCH, the UE consumes battery power. It should therefore be appreciated by those skilled in the art that such a basic DRX operation may not always be efficient, particularly if a UE frequently does not receive any signals (i.e. any PDCCHs with RNTIs addressed to that UE) during the ON period of the DRX operation. It is therefore desirable to wake the UE up only when there is a paging message actually targeted at the UE in the given paging occasion i.e., when the particular UE is being paged. Wake-up Signals to Save Power

[0059] There are a number of different ways in which the battery life of a UE may be improved. One such way is by enabling a DRX configuration to adapt to a UE’s expected data reception or transmission profile. For example, a Wake-Up Signal (WUS) may be used to indicate whether a UE should wake up during a DRX ON period. The WUS is a signal or a channel that is transmitted to a UE or a group of UEs prior to a DRX ON period or Paging Occasion (PO) to indicate whether the UE(s) needs to wake up during this ON period and monitor for possible traffic, e.g. monitor the PDCCH. Using a WUS signal in this way to wake-up a UE recognises that not every DRX ON period contains traffic for the UE, and for such a case, the PDCCH monitoring consumes unnecessary power from the UE, which can be avoided with this WUS signaling.

[0060] Wake-up signals are supported in technologies such as eMTC, NB-loT and in 5G NR. The eMTC I NB-loT wake-up signal (WUS) is used in IDLE mode before a paging occasion. If the UE detects a WUS, it wakes up and monitors the following paging occasion for an MTC PDCCH (MPDCCH) or an NB-loT (NPDCCH) that may further allocate a paging message. If the UE does not receive a WUS, it can go back to sleep. The WUS consists of a known sequence. The UE can monitor for the WUS by performing a correlation against this known sequence. As indicated above, the WUS either can be common to all the UEs associated with the paging occasion, or can be associated with a group of UEs that are associated with the paging occasion.

[0061] An example of a WUS is illustrated by a timing diagram showing a plot of transmission power and UE receiver activity with respect to time provided in Figure 5. As shown in Figure 5, a wake-up signal WUS 51 occurs at a known time offset (T2- TI) 52 before a paging occasion 54. The time offset 52 allows the UE to “boot-up” its main receiver (MR) after WUS reception and before the paging occasion 54. As a result the WUS itself can be monitored with a lower power receiver, since the lower power receiver does not need to be able to receive all the features of the signal that the MR is able to receive. The WUS is transmitted prior to the paging occasion 54 as shown in Figure 5 at time TI, only when there is an MPDCCH transmission in the paging occasion 54. The MDPCCH transmission in the paging occasion 54 allocates a PDSCH transmission between time T3and T4. The PDSCH transmission comprises paging information such as the Temporary Mobile Subscriber Identity (TMSI) of a UE. The PDSCH transmission allocated by the MDPCCH may be inside or outside the paging occasion 54. When the WUS is UE-specific (i.e. each UE has its own WUS), the WUS for that UE is only sent when there is an MPDCCH in a paging occasion which allocates a PDSCH that is targeted at that UE. When the WUS is group-specific (i.e. a group of UEs share a WUS), the WUS for that group is sent when there is an MPDCCH in a paging occasion which allocates a PDSCH that is targeted to at least one of the UEs in that group. Upon detection of a WUS, the UE will proceed to-fine tune its frequency and timing tracking loops if required and blind detects for an MPDCCH between time T2and T3followed by decoding of the PDSCH carrying the paging information between time T3and T4. If the UE fails to detect a WUS, it will go back to sleep and skip detecting for MPDDCH. Hence by using WUS, the UE will consume less energy by avoiding unnecessary monitoring of MPDCCH. It should be appreciated that WUS can also be used in connected mode when DRX is used. The paging functionality discussed above has been described with respect to LTE-M / eMTC operation, where the paging PDSCH is allocated using an MPDCCH. Those skilled in the art would appreciate that operation in 5G / NR is similar.

[0062] For the example of 5G NR, a wake-up signal WUS is used in CONNECTED mode DRX operation as described in [3], the contents of which are hereby incorporated by reference in their entirety. The 5G NR WUS is based on a PDCCH that carries Downlink Control Information (DCI) format 2_6. The PDCCH may be referred to as Power saving-PDCCH (PS- PDCCH), while the monitoring period for this PDCCH is referred to as a PS-PDCCH monitoring period. Here, the term PS-PDCCH is synonymous with “DCI format 2_6 with CRC scrambled by PS-RNTI”. This monitoring period may also be referred to as a “power saving monitoring period”. The procedure for monitoring DCI format 2_6 is described in detail in section 10.3 of [4], the contents of which are hereby incorporated by reference in their entirety. The NR WUS is described in more detail in [5], the contents of which are hereby incorporated by reference in their entirety.

[0063] An example timing diagram illustrating a transmission of signals with respect to time for a 5G NR operation in CONNECTED mode is shown in Figure 6. As shown in Figure 6, a PS- PDCCH 61 occurs in a search space before a DRX_ON phase 62 of a DRX cycle represented by a double headed arrow 64. This example represents one full CONNECTED mode DRX cycle. A temporal location of the PS-PDCCH 61 is in advance of the DRX_ON phase 62 by an amount ps_Offset 66. A UE decodes the DCI format 2_6 within the PS-PDCCH. Since the UE only has to decode the PS-PDCCH, it does not have to operate its full receiver circuitry, and therefore PS-PDCCH can be decoded with a lower receive power. If the DCI indicates that the UE should wake up, the UE wakes up its full receiver circuitry for the next DRX_ON duration 62. Otherwise the UE can go to sleep following the PS-PDCCH and does not have to decode other PDCCH during the DRX_ON duration 62. The UE needs to monitor for PS- PDCCH during a monitoring window, where the monitoring window starts at a known time before the start of the DRX_ON period and ends at a time ps_Offset before the start of the next DRX_ON period.

[0064] At the time of filing of the present disclosure, 3GPP has completed a study item [6], which is hereby incorporated for reference in its entirety, on low power receivers and low power wakeup signals for NR-5G. This study item had the following objectives:

[0065] • Identify evaluation methodology (including the use cases) & key performance indicators [RAN1];

[0066] • Study and evaluate low-power wake-up receiver architectures [RAN1 , RAN4];

[0067] • Study and evaluate wake-up signal designs to support wake-up receivers [RAN1 , RAN4]; • Study and evaluate L1 procedures and higher layer protocol changes needed to support the wake-up signals [RAN2, RAN1]; and

[0068] • Study potential UE power saving gains compared to the existing Rel-15 / 16 / 17 UE power saving mechanisms, the coverage availability, as well as latency impact of low- power WUR / WUS. System impact, such as network power consumption, coexistence with non-low-power-WUR UEs, network coverage / capacity / resource overhead should be included in the study [RAN1],

[0069] The justification of the study, as described in section 3 of [6], is reproduced below.

[0070] 5G systems are designed and developed targeting for both mobile telephony and vertical use cases. Besides latency, reliability, and availability, UE energy efficiency is also critical to 5G. Currently, 5G devices may have to be recharged per week or day, depending on an individual’s usage time. In general, 5G devices consume tens of milliwatts in RRC idle / inactive state and hundreds of milliwatts in RRC connected state. Designs to prolong battery life therefore are a necessity for improving energy efficiency as well as for providing a better user experience.

[0071] Energy efficiency is even more critical for UEs without a continuous energy source, e.g., UEs using small rechargeable and single coin cell batteries. Among vertical use cases, sensors and actuators are deployed extensively for monitoring, measuring, charging, etc. Generally, their batteries are not rechargeable and are expected to last for at least a few years. Such UEs may be wearable devices which may include smart watches, rings, eHealth related devices, and medical monitoring devices. With typical battery capacities, it is challenging to sustain power for up to one or two weeks as required.

[0072] The power consumption depends on the configured length of wake-up periods, e.g., on the paging cycle. To meet the battery life requirements noted above, eDRX cycles of long durations are expected to be used, resulting in high latency, which is not suitable for services with requirements of both long battery life and low latency. For example, in fire detection and extinguishment use cases, fire shutters should be closed and fire sprinklers should be turned on by the actuators within one or two seconds from the time the fire is detected by sensors; a long eDRX cycle therefore cannot meet the delay requirements. eDRX thus appears not to be suitable for latency-critical use cases. Therefore, the intention is to study ultra-low power mechanisms that can support low latency in Rel-18, e.g. lower than eDRX latency.

[0073] Currently, UEs need to periodically wake up once per DRX cycle, which dominates the power consumption in periods with no signalling or data traffic. If UEs are able to wake up only when they are triggered, e.g. via paging, power consumption could be dramatically reduced. This can be achieved by using a wake-up signal (WUS) - as described above - to trigger the main radio, and a separate receiver at the UE which has the ability to monitor for wake-up signals with ultra-low power consumption without needing to power-up the main receiver (MR). The MR is relatively high power consuming, which handles the normal communication with the gNB and works for data transmission and reception, and can be turned off or set to deep sleep unless it is turned on.

[0074] The power consumption for monitoring wake-up signal depends on the wake-up signal design and the hardware module of the wake-up receiver used for wake-up signal detection and processing. The study in [6] was to primarily target low-power WUS and wake-up receiver (WUR) for power-sensitive, small form-factor devices including loT use cases (such as industrial sensors, controllers) and wearable devices. Other use cases are not precluded, e.g. extended Reality (XR) / smart glasses, smart phones, etc.

[0075] The goal was hence to support a low power wake up signal (LP-WLIS) that is received by a low power wake-up receiver (LP-WLIR). If the LP-WLIR detects an LP-WLIS in between DRX ON occasions, while the main receiver (MR) of the UE is kept asleep, the MR is woken up by a signal transmitted from the LP-WLIR (i.e. a wake-up command), so that the MR can then listen for a paging message in the following paging occasions, and the MR can then subsequently decode any data that is transmitted by the network. Therefore, if the WUS is only transmitted shortly before paging occasions in which the target UE is paged, the MR will be woken up only when an actual paging message targeted at the UE is present in the following paging occasions. This stops the UE MR from waking up to needlessly search for a paging message during paging occasions when the network has not paged the UE, thereby reducing further battery power consumption. A WUS can also be transmitted prior to paging occasions in which the UE is paged for other reasons such as TAU etc.

[0076] Figure 7 shows the relationship between the MR 71 and LP-WUR 72 of a UE. The LP-WUR 72 receives a signal, RX_sig2, and monitors for LP-WUS within RX_sig2. If the LP-WUR 72 detects an LP-WUS, it wakes up the MR 71 via a wake-up command 73, which may for example be an “ON I OFF” indication. The MR 71 then decodes its input signal, RX_sig1 , and receives data 74 which can then be forwarded to the UE’s buffers or processors or the like. In some cases, RX_sig2 is the same as RX_sig1 . For example, RX_sig1 and RX_sig2 can both occur within the system bandwidth of an NR waveform. In other cases, RX_sig1 and RX_sig2 are different. For example, RX_sig1 could be within the system bandwidth of an NR waveform while RX_sig2 could have a narrower bandwidth that is an in or out of band signal.

[0077] In IDLE mode, the LP-WUS can be used to wake up the MR so that the UE can monitor a paging occasion (PO). That is:

[0078] • If an LP-WUS is detected, the UE wakes up MR and the UE decodes the PO; or

[0079] • If an LP-WUS is not detected, the MR is not woken up. Figure 8 shows the case where an LP-WLIS 81 is used to wake an IDLE mode UE up to monitor for a paging message during a paging occasion (PO). The LP-WLIR of the UE monitors for an LP-WUS 81 during an LP-WUS monitoring window. The LP-WUR of the UE knows that if the network were to transmit an LP-WUS 81 , it would be transmitted during the LP-WUS monitoring window. Hence, the LP-WUR only needs to actively monitor for LP-WUS 81 during this LP-WUS monitoring window. If LP-WUS 81 is detected, the LP-WUR wakes the MR up (those skilled in the art would appreciate that this process may take some time, for example 100ms). The MR then synchronises to the downlink and monitors for PDCCH 82 during the paging occasion. If the UE receives a PDSCH 83 containing its identifier during the PO, the UE performs an initial access procedure with the network. During the time that the MR wakes up, the MR needs to synchronise with the network and potentially read system information. It should be appreciated here that if an LP-WUS is not detected, the LP-WUR does not need to wake up the MR.

[0080] Some LP-WUR architectures have sufficiently low power consumption that they can be “ON” all the time. Other LP-WURs have a higher power consumption, or are implemented in UEs which require lower power consumption, and it is therefore advantageous for those LP-WUR to only monitor for LP-WUS in an LP-WUS monitoring window (i.e. in a DRX-like fashion).

[0081] For brevity, low-power receivers (LPRs) for receiving a WUS (i.e. LP-WURs) will be referred to hereafter as LPRs. Similarly, a WUS received by an LPR (i.e. an LP-WUS) will be hereafter referred to as a “WUS”.

[0082] The implementation of LPRs is expected to reduce communications device energy consumption and therefore provide energy savings. However, the implementation of LPRs involves various technical challenges, for example:

[0083] — In order for an LPR of a UE to efficiently detect a WUS with a low misdetection rate, the LPR should remain relatively synchronised to the gNB transmitting the WUS. This is particularly important if the WUS is transmitted at predefined times, or within predefined time windows, such as a time or time window shortly before DRX ON occasions of the UE. In such cases, the LPR needs to be relatively synchronised to the gNB in order to keep track of the DRX ON occasions. If the UE remains in RRC- IDLE mode during which the MR is asleep for extended periods, the UE’s clock may drift. Furthermore, UE mobility may also cause significant frequency offsets. Relatively good synchronisation also reduces the false alarm rate. The LPR attempts to decode for a potential WUS every time that a WUS may have been transmitted. Every decoding attempt leads to the potential for a false alarm. If synchronisation is poorer, the LPR attempts to decode for a potential WUS over a wider time window, due to the timing uncertainty. The wider time window means that more decoding attempts are required and the false alarm rate increases.

[0084] — The MR is usually configured to wake up to carry out RRM measurements during RRM measurement windows / events. However, the use of the MR to perform RRM measurements leads to high power consumption.

[0085] — Receiving and decoding WUS signalling. The WUS may comprise: a cell ID of the cell in which the WUS is transmitted, the UE group or UE ID to which the WUS is targeted etc. As such, a technical problem to solve is hence how to provide as low complexity an LPR as possible, that enables a communications device to increase its power-saving capabilities, whilst still properly accomplishing the functions detailed above relating to synchronisation, performance of measurements, and properly receiving and decoding WUS signalling. Embodiments of the present technique therefore seek to provide solutions to address such a problem.

[0086] LPR Synchronisation

[0087] Figure 9 shows a part schematic, part message flow diagram representation of a wireless communications system comprising a communications device (e.g. a UE) 101 and an infrastructure equipment (e.g. a gNB) 102 of a wireless communications network in accordance with at least some embodiments of the present technique. The communications device 101 is configured to transmit signals to and / or receive signals from the wireless communications network, for example, to and from the infrastructure equipment 102 of the wireless communications network. Specifically, the communications device 101 may be configured to transmit data to and / or receive data from the wireless communications network (e.g. to / from the infrastructure equipment 102) via a wireless radio interface provided by the infrastructure equipment 102 (e.g. a Uu interface between the communications device 101 and a Radio Access Network (RAN), which includes the infrastructure equipment 102). The communications device 101 comprises a main receiver (or main receiver circuitry) 101.1 , a low-power receiver (or low-power receiver circuitry) 101.2 and at least one controller (or controller circuitry) 101.3, 101.4. Although not shown, the communications device 101 may comprise a transmitter (or transmitter circuitry). The infrastructure equipment 102 comprises a transceiver (or transceiver circuitry) 102.1 , and a controller (or controller circuitry) 102.2. The transceiver may comprise a separate transmitter and receiver, or may be a component configured to operate as both a transmitter and a receiver. Similarly, the transceiver circuitry may comprise separate transmitter circuitry and receiver circuitry, or may be circuitry configured to operate as both a transmitter circuitry and receiver circuitry. Each of the controllers 101.3, 101.4, 102.2 may be, for example, a microprocessor, a CPU, or a dedicated chipset, etc. In the example of Figure 9, two controllers 101.3, 101.4 are shown in the communications device 101 , with a first controller 101.3 operatively coupled to (and hence controlling) the main receiver 101.1 , and a second controller 101.4 operatively coupled to (and hence controlling) the low-power receiver 101.2. Those skilled in the art would appreciate that this would be advantageous given that the main CPU (e.g. controller 101.3) of the communications device 101 may be more powerful than a CPU (e.g. controller 101.4) connected to the low-power receiver 101.2 and would consume a lot of power if it needed to be on so as to control the low-power receiver 101.2. Of course those skilled in the art would appreciate that in some arrangements of embodiments of the present technique, the communications device 101 may comprise a single controller (or controller circuitry) used to control both of the main receiver 101.1 and the low-power receiver 101.2.

[0088] The main receiver (MR) 101.1 may be configured to operate in an ON state in which the MR

[0089] 101.1 can receive signals from the infrastructure equipment 102 or in an OFF state in which the MR 101.1 cannot receive signals from the infrastructure equipment 102. Similarly, the low- power receiver (LPR) 101.2 may be configured to operate in an ON state in which the LPR

[0090] 101.2 can receive signals from the infrastructure equipment 102 or in an OFF state in which LPR 101.2 cannot receive signals from the infrastructure equipment 102. The MR (or LPR) may be regarded as “awake” in the ON state and “asleep” in the OFF state. A power consumption of the LPR 101.2 when the LPR 101.2 is in the ON state is lower than a power consumption of the MR 101.1 when the MR 101.1 is in the ON state. There may be a plurality of types of “OFF” state comprising, for example, a light sleep state, a deep sleep state and an ultra-deep sleep state. References to an MR being in “OFF” state may therefore mean that the MR 101.1 is in the light sleep state, deep sleep state or the ultra-deep sleep state. However, the present disclosure is not so limited, and references to the MR 101.1 being in an OFF state may be referring to any state of the MR 101.1 which consumes less power than when the MR 101.1 is in the ON state. In the light steep state, the MR 101.1 circuitry may be powered on, synchronised and ready to communicate. In the light sleep state, the MR 101.1 may retain data in its memories and keep its clock ticking along, for example. Transitioning the MR 101.1 in and out of the light sleep state is fast. In the deep sleep state, the circuitry of the MR 101.1 may be switched on, but the MR 101.1 is not synchronised to the network. In the ultra-deep sleep state, the circuitry of the MR 101.1 may be completely switched off. In this case, transitioning the MR 101.1 to the ON state may comprise booting a CPU of the MR 101.1 , and loading information into RAM, for example. Transitioning the MR 101.1 out of the ultra-deep sleep state takes longer than for the light sleep state, but more power is saved in the ultra-deep sleep state. Transitioning the MR 101.1 out of the deep sleep state takes longer than transitioning the MR 101.1 out of the light sleep state but takes less time than transitioning the MR 101.1 out of ultra-deep sleep state.

[0091] The LPR 101.2 may alternatively be referred to as a low-power (LP) wake-up signal receiver (LP-WUR).

[0092] In some embodiments, the communications device 101 may be in an RRC IDLE or RRC CONNECTED state during the process described in Figure 9.

[0093] In Figure 9, steps 104, 106, 108 and 110 are performed while the LPR 101.2 is in the ON state. In steps 104, 106, 108 and 110 the MR 101.1 may be in the ON state or the OFF state. In particularly advantageous embodiments, the MR 101.1 is in the OFF state during at least steps 108 and 110. In step 112, the MR 101.1 is in the ON state. In step 112, the LPR 101.2 may be in the ON or OFF state.

[0094] As shown in the example of Figure 9, in step 104, the controller 101.4 is configured to control the LPR 101.2 to receive one or more synchronisation signals (SSs) from the infrastructure equipment 102 in one or more predefined SS reception periods. The SS reception periods are predefined in the sense that they are known to the communications device 101. In some embodiments, the SS reception periods may be periodic. The LPR 101.2 is configured to acquire both time and frequency synchronisation based on the one or more SSs. The one or more SSs received by the LPR 101.2 may be referred to as “low-power synchronisation signals (LPSSs)”. In other words, low-power synchronisation signals are referring to synchronisation signals that can be read by an LPR. It should be noted that a transmit power of LPSs may not necessarily be lower than a transmit power of other SSs.

[0095] In some embodiments, each of the one or more SSs is a random sequence comprised in a different Orthogonal Frequency Division Multiplexing (OFDM) symbol of the wireless radio interface. The random sequence in each OFDM symbol may be acquired by the LPR 101.2 in the time and / or frequency domain. In cases where the random sequence is an inverse Discrete Fourier Transform (IDFT) in the time domain of the OFDM symbol comprising the random sequence, sliding correlation may be used to provide a timing offset of the random sequence while sub-bin frequency domain correlation may be used to obtain a frequency offset of the random sequence. In some embodiments, the one or more SSs are Primary Synchronisation Signals (PSSs) also used to synchronise the MR 101.1 with the infrastructure equipment 102. For example, a PSS may be comprised in a synchronisation signal block (SSB) transmitted by the infrastructure equipment 102 to the communications device 101. In such cases, a bandwidth over which the LPR 101.2 is configured to receive signals from the infrastructure equipment 102 is equal to or greater than a bandwidth of the SSBs.

[0096] Embodiments where the one or more SSs are Primary Synchronisation Signals (PSSs) used to synchronise the MR 101.1 with the infrastructure equipment 102 have at least the following technical advantages:

[0097] — Communications resource utilisation efficiency is increased. Since the same PSSs are already used to synchronise the MR 101.1 with the infrastructure equipment 102, additional communications resources are not required to synchronise the LPR 101.2 with the infrastructure equipment 102.

[0098] — Reduced specification impact. Since PSSs are already used to synchronise the MR 101.1 with the infrastructure equipment 102, 3GPP specifications will only need minor (if any) modifications to specify that the PSS is also used to synchronise the LPR 101.2.

[0099] — Algorithms currently used for PSS detection by the MR 101.1 can be re-used for PSS detection by the LPR 101.2.

[0100] — Measurement Aid. Each PSS is associated with a cell group ID (NID(2)). Therefore, detecting the PSS allows the LPR 101.2 to determine the cell group. Accordingly, the cell group can be determined with less power and with existing algorithms. The detection of the PSS and the determination of the cell group may be performed as a one step process.

[0101] — Coverage for the PSS used for synchronising the LPR 101.2 and the MR 101.1 is the same.

[0102] — If the PSS changes bandwidth (for example, because of a change in sub-carrier spacing used for SSBs in the cell), the bandwidth of the WUS may change accordingly. Therefore, the LPR 101.2 may be configured to accommodate different bandwidths of SSB.

[0103] In step 106, at least one of the controllers 101.3, 101.4 controls the communications device 101 to synchronise the LPR 101.2 with the infrastructure equipment 102 based on the one or more received SSs. The synchronisation may comprise, for example, detecting and correcting timing and frequency errors based on the one or more received SSs.

[0104] In step 108, at least one of the controllers 101.3, 101.4 controls the synchronised LPR 101.2 to monitor one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment 102.

[0105] In step 110, the synchronised LPR 101.2 may receive a WUS in one of the WUS monitoring periods. If the synchronised LPR 101 .2 receives a WUS in one of the WUS monitoring periods, then the method proceeds to step 112. In some embodiments, if the MR 101.1 is in the OFF state and the synchronised LPR 101.2 receives a WUS in one of the WUS monitoring periods, at least one of the controllers 101.3, 101.4 controls the MR 101.1 to transition from the OFF state to the ON state before proceeding to step 112. In some embodiments, the MR 101.1 may already be in the ON state for a different purpose. For example, the MR 101.1 may be performing measurements on a neighbouring cell while the LPR 101.2 is monitoring for the WUS in a serving cell. In step 112, while the MR 101.1 is in the ON state, at least one of the controllers 101.3, 101.4 controls the MR 101.1 to monitor a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment 102. The downlink signal monitoring period is subsequent to the WUS monitoring period in which the WUS was received.

[0106] The WUS received by the LPR 101.2 may be alternatively referred to as a low-power WUS (LP-WUS) because it is a WUS received by the LPR 101.2.

[0107] The downlink signal monitoring period may be, for example, a paging occasion for the communications device 101 (such as paging occasion 54) or a DRX_ON period (such as DRX_ON duration 62).

[0108] By synchronising the LPR 101.2 with the infrastructure equipment 102, the communications device 101 can efficiently detect a WUS with a low rate of misdetection and a low rate of false alarms.

[0109] An example of synchronising the LPR 101.2 based on one or more SSs is shown in Figure 10A. While the LPR 101.2 is in the ON state and the MR 101.1 is in the OFF state, the communications device 101 receives an SS in an SS reception period 202 using its LPR 101.2. The communications device 101 uses the received SS to synchronise the LPR 101.2 with the infrastructure equipment 102. Then, while the LPR 101.2 is in the ON state and the MR 101.1 is in the OFF state, the LPR 101.2 monitors a WUS monitoring period 204 for reception of a WUS from the infrastructure equipment 102. In the example shown in Figure 10A, a WUS is received by the LPR 101.2 in the WUS monitoring period. Therefore, the communications device 101 transitions the MR 101.1 from the OFF state to the ON state to monitor a downlink signal monitoring period 206. As shown in Figure 10A, the downlink signal monitoring period 206 is subsequent to the WUS monitoring period 204 in which the WUS was received by the LPR 101.2.

[0110] Another example of synchronising the LPR 101.2 based on one or more SSs is shown in Figure 10B. While the LPR 101.2 is in the ON state, the communications device 101 receives a first SS in a first SS reception period 208. The communications device 101 uses the first SS to synchronise the LPR 101.2 with the infrastructure equipment 102. Then, while the LPR 101.2 is in the ON state and the MR 101.1 is in the OFF state, the communications device 101 monitors a first WUS monitoring period 210 for reception of a WUS from the infrastructure equipment 102. In the example shown in Figure 10B, a WUS is not received by the LPR 101.2 in the first WUS monitoring period 210. Therefore, the communications device 101 does not transition the MR 101.1 from the OFF state to the ON state. In other words, the MR 101.1 remains in the OFF state. In some examples, as shown in Figure 10B, the communications device 101 receives a second SS in a second SS reception period 212. The communications device 101 uses the second SS to synchronise the LPR 101.2 with the infrastructure equipment 102. The communications device 101 uses the synchronised LPR 101.2 to monitor a second WUS monitoring period 214 for reception of a WUS from the infrastructure equipment 102. In the example shown in Figure 10B, a WUS is received by the LPR 101.2 in the second WUS monitoring period 214. Therefore, the communications device 101 transitions the MR 101.1 from the OFF state to the ON state to monitor a downlink signal monitoring period 216. As shown in Figure 10B, the downlink signal monitoring period 216 is subsequent to the WUS monitoring period 214 in which the WUS was received by the LPR 101.2. In some embodiments, the second SS reception period 212 may be between the first SS reception period 208 and the first WUS monitoring period 210. In this case, the communications device 101 synchronises the LPR 101.2 with the infrastructure equipment 102 using the first SS received in the first SS reception period 208 and the second SS received in the SS reception period. For example, the communications device 101 may perform one synchronisation using both the first and second SS, or may synchronise the LPR 101.2 using the first SS and then re-synchronise the LPR 101.2 using the second SS.

[0111] In some embodiments, the second SS reception period may not be present. In this case, the communications device 101 uses the LPR 101.2 as synchronised based on the first SS received in the first SS reception period 208 to monitor the second WUS monitoring period 214.

[0112] In the examples shown in Figures 10A and 10B, the LPR 101.2 may be in the ON state for the duration shown. For example, the LPR 101.2 may always be in the ON state while the communications device 101 is powered on. However, it will be appreciated that the LPR 101.2 may transition to the OFF state for periods during the duration shown (for example, during periods when the LPR 101.2 is not expected to receive signals from the infrastructure equipment 102) as long as the LPR 101.2 is in the ON state when it is required to monitor for signals from the infrastructure equipment 102 (such as during SS reception periods and WUS monitoring periods).

[0113] In some embodiments, the SS reception periods may be periodic. Accordingly, the LPR 101.2 is periodically synchronised with the infrastructure equipment 102, therefore keeping the synchronising up-to-date and increasing power saving.

[0114] Reference has been made here to “first” and “second” SS reception periods and WUS monitoring periods. These have been used as labels to specify the order in which the SS reception periods or WUS periods are monitored. For example, the second WUS period is monitored after the first WUS period. Although in some examples, the “first” SS reception period (or WUS monitoring period) is referring to the first SS reception period (or WUS monitoring period) in time monitored by the LPR 101.2, in other examples the first SS reception period (or WUS monitoring period) is referring to an SS reception period (or WUS monitoring period) later in time than the first monitored SS reception period (or first monitored WUS monitoring period), as long as the first SS reception period (or WUS monitoring period) is monitored before the second SS reception period or (WUS monitoring period).

[0115] In some embodiments, the SS reception periods are configured independently from the WUS monitoring periods. In other embodiments, the SS reception periods are configured along with the WUS monitoring periods. For example, the SS reception periods may be configured by the infrastructure equipment 102 such that an SS reception period occurs prior to each WUS monitoring period.

[0116] Radio Resource Management (RRM) Measurements by the LPR

[0117] In some embodiments, a bandwidth over which the LPR 101.2 is configured to receive signals from the infrastructure equipment 102 is equal to or greater than a bandwidth of SSBs transmitted by the infrastructure equipment 102. The SSBs may be used for synchronising the MR 101.1 with the infrastructure equipment 102 or, as explained above, the SSBs may be used for synchronising the LPR 101.2 and / or the MR 101.1 with the infrastructure equipment 102. In embodiments where a bandwidth over which the LPR 101 .2 is configured to receive signals from the infrastructure equipment 102 is equal to or greater than a bandwidth of SSBs transmitted by the infrastructure equipment 102, the LPR 101.2 may be configured to receive one or more SSBs from the infrastructure equipment 102 and perform one or more Radio Resource Management (RRM) measurements on the one or more SSBs. For example, the LPR 101.2 may perform a reference signal received power (RSRP) measurement and / or a reference signal received quality (RSRQ) measurement on the one or more SSBs received from the infrastructure equipment 102. The RRM measurements may be used by the communications device 101 to assist in mobility. For example, the communications device 101 may determine, based on the RRM measurements, whether to remain camped on the serving cell or to handover to a different cell. In some embodiments, the communications device 101 may remain camped on the serving cell if the RSRP of one or more of the SSBs measured by the LPR 101.2 is above a threshold. In some embodiments, where the RSRP of the one or more SSBs received by the LPR 101.2 is below a threshold, one of the controllers 101.3, 101.4 may command the MR 101.1 to transition from the OFF state to the ON state. In such cases, or if the MR 101.1 is already in the ON state, the MR 101.1 may measure the RSRP of one or more subsequent SSBs from neighbouring cells. Then, based on the RSRP measurements of the neighbouring cells, the communications device 101 may determine to handover to one of the neighbouring cells. For example, the communications device 101 may determine to handover to the neighbouring cell with the highest RSRP measurement. As will be understood by one skilled in the art, in existing systems, RRM measurements are performed on SSBs by the MR 101.1. By configuring the LPR 101.2 to perform RRM measurements on SSBs, the RRM measurements can be determined earlier (for example, before the MR 101.1 wakes up). Furthermore, the use of the LPR 101.2, rather than the MR 101.1 , to perform RRM measurements reduces power consumption. When performing measurements on one or more of the SSBs, the LPR 101.2 may only perform measurements on portions of an SSB. For example, the LPR 101.2 may perform measurements on a PSS portion of the SSB. By not requiring the LPR 101.2 to perform measurements on the whole SSB, the complexity of the LPR 101.2 is reduced (for example, the LPR 101.2 does not need to be able to decode I receive the SSS and I or the PBCH).

[0118] Composition of the LP-WUS

[0119] The infrastructure equipment 102 of the wireless communications network configures communications resources which can be used for the transmission of the WUS (“WUS resources”). For example, the infrastructure equipment 102 configures the WUS monitoring periods. In some examples, a bandwidth of the WUS resources is equal to or larger than an NR SSB bandwidth of 20 resource blocks (RBs). The WUS resources may be configured at regular intervals within a bandwidth part that also carries one or more SSBs. The configuration of the WUS resources can be read by the MR 101.1 from system information transmitted by the infrastructure equipment 102. The configuration of the WUS resources may be configured into the LPR 101.2 by the MR 101.1. In other words, the configuration of the WUS resources may be communicated from the MR 101.1 to the LPR 101.2 via circuitry in the communications device 101. Alternatively, the LPR 101.2 may receive the configuration of the WUS resources via a direct signal from the infrastructure equipment 102. The MR 101.1 may also decode the one or more SSBs received from the infrastructure equipment 102 to determine an identity of the cell provided by the infrastructure equipment 102 which the communications device 101 is located in. For example, the MR 101.1 may determine a physical cell identity (PCID) of the cell. Detailed methods for configuring the WUS resources are described in [7], the contents of which are hereby incorporated by reference in their entirety.

[0120] In some examples, the WUS monitoring periods for a particular communications device 101 are configured to be just before downlink signal monitoring periods for the communications device 101. For example, the infrastructure equipment 102 may configure a plurality of periodic WUS monitoring periods such that each WUS monitoring period is just before a respective one of a plurality of periodic downlink signal monitoring periods. As explained above, the downlink signal monitoring periods may be paging occasions, for example. The paging occasion may be determined by the communications device 101 , for example, using a combination of information broadcast by the infrastructure equipment 102 in SIB1 and a 5G S-Temporary Mobile Subscriber Identity (TMSI) for the communications device 101.

[0121] A WUS may be transmitted in a plurality of OFDM symbols in the configured WUS resources. The plurality of OFDM symbols in which a WUS is transmitted will be hereafter referred to as “WUS symbols”. In some embodiments, a WUS may be transmitted in (1+N) WUS symbols, where a first of the WUS symbols is an identification symbol and the N subsequent symbols of the WUS symbols are data-carrying symbols.

[0122] In some embodiments, the N data-carrying WUS symbols are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence, such as a Zadoff-Chu (ZC) sequence, as illustrated in Figure 11.

[0123] In some embodiments, the 1+N WUS symbols are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence, such as a Zadoff-Chu (ZC) sequence. The identification symbol can be received either by prior knowledge of the ZC sequence (e.g. via configuration in SIB or knowledge of the ZC sequence as a function of a UE parameter, such as the S-TMSI) or by blind decoding for the ZC sequence.

[0124] The PSS m-sequence may be represented by “P(k)”, where k = 0,1,2, , .NSC- 1, where Nscis the number of sub-carriers or resource elements used for the WUS in a WUS symbol.

[0125] The ZC sequence may be represented by “Z(k)”, where k = 0,1,2, . . Nsc- 1, where Nscis the number of sub-carriers or resource elements used for the WUS in a WUS symbol. Z(k) may obey Equation 1 below.

[0126] .rjrfc(fc+l)

[0127] Equation 1 . S( / c) = e1 Nzc

[0128] Where Nzc = 144, for example, and r is a root of the ZC sequence.

[0129] Figure 11 illustrates an example of a WUS symbol in the frequency domain. In the example shown in Figure 11 , the WUS symbol comprises a plurality (L) of resource blocks which have been modulated by a sequence formed by the dot product of the PSS m-sequence and a ZC sequence and a plurality (D) of resource elements on either side of the L resource blocks which have been modulated with zero. The D resource elements which have been modulated with zero act as band gaps for mutual protection of the WUS and other surrounding downlink transmissions. In the example shown in Figure 11 , L = 12 resource blocks and D = 48 resource elements on either side of the L resource blocks. Since each of the L = 12 resource blocks comprise 12 resource elements, then the L = 12 resource blocks are made up of 144 resource elements. As shown in the example of Figure 11 , there are 144 / 2 = 72 resource elements of the L = 12 resource blocks on either side of the centre frequency The subcarrier at the centre frequency is not modulated.

[0130] The multiplication (dot product) of the second sequence (such as a ZC sequence) with the PSS m-sequence ensures that existing UEs do not detect the WUS as a PSS. This allows the PSS to be efficiently re-used for synchronising the LPR 101.2 without negatively impacting existing UEs. The LPR 101.2 can still receive the WUS with the same circuitry as the circuitry used for detection of the PSS. For example, when trying to detect PSS, the LPR 101 .2 circuitry can be programmed with a PSS-based sequence to correlate against; and when trying to detect WUS, the LPR 101.2 circuitry can be programmed with the dot product of the PSS m- sequence and the ZC sequence. The fundamental correlation is related in either case. In some embodiments, the WUS itself can be used for synchronisation of the LPR 101 .2. thereby providing efficient synchronisation of the LPR 101.2

[0131] The identification symbol may allow the LPR 101.2 to detect the ZC used in the WUS. In some embodiments, the identification symbol may comprise an indication of a number of the N data- carrying symbols in the WUS. In some embodiments, the number of the N data-carrying symbols in the WUS is indicated by a time domain cyclic shift of the identification symbol. When the range of possible values for N is small, there are only a few possible cyclic shifts that can be applied to the identification WUS symbol of the WUS. This reduces the number of blind decodes at the LPR 101.2. The value of N may be determined according to an acceptable amount of resource overhead for the WUS. The value of N may also be determined according to an amount of information that is to be signalled in the WUS (for example, whether UE-IDs need to be signalled in the WUS). The value of N may also be determined by an amount of repetition that is required in the WUS, which is based on a coverage requirement of the WUS. Although embodiments have been described where only one identification symbols is used, it will be appreciated that in other embodiments there may be two or more identification symbols. In such embodiments, a larger number of values may be signalled. In some embodiments, each of the data-carrying symbols indicates the data carried by that symbol using a time domain cyclic shift of that data-carrying symbol.

[0132] As mentioned above, the identification symbol may allow the communications device 101 to detect the ZC used in the WUS. However, in some embodiments, there may be a plurality of periodic WUS monitoring periods each with a different index configured, and the indexes indicate the ZC used for a WUS in the respective WUS monitoring periods. The communications device 101 may determine the indexes of the WUS monitoring period it should monitor based on, for example, an S-TMSI of the communication device. When the communications device 101 determines to monitor a WUS monitoring period, the communications device 101 may determine the ZC used for the WUS in the WUS monitoring period based on the index of the WUS monitoring period. Therefore, the communications device 101 knows which ZC to monitor within the WUS monitoring period.

[0133] This helps to reduce false alarm rates in the performance of the LPR 101.2. In such embodiments, the identification symbol does not need to indicate the ZC of the WUS.

[0134] In some embodiments, the N data-carrying symbols subsequent to the identification symbol are modulated according to the same P(k)*S(k) sequence in the frequency domain but are cyclically shifted in the time domain prior to transmission. The allowed amount of cyclic shift is 128, thereby allowing each of the N data-carrying symbols to carry up to 7 bits of data. Therefore, the N data-carrying symbols can carry 7N bits of data to the communications device 101 via the WUS.

[0135] The 7N bits may be used to indicate one or more parameters. The one or more parameters comprise:

[0136] — a part of a cell ID. For example, the parameters may comprise an NID(1)part of a cell ID requiring 9 bits. The communications device 101 may combine an NID(2)part of the cell ID received by the LPR 101.2 and / or MR 101.1 from the PSS to get the full cell ID of the cell that transmits the WUS. The Cell ID is useful for identifying what cell the WUS is transmitted from and is especially useful for the purpose of RRM measurements; and / or

[0137] — an identity of the communications device 101. This may enable the WUS to discriminate between different communications devices. For example, only the communications devices whose identity is indicated may transition their MR 101.1 to the ON state on detection of the WUS. This reduces power consumption because not all of the communications devices need to transition their MR 101 .1 to the ON state on detection of a WUS. For example, some RRC-IDLE mode UEs may not need to transition their MR 101.1 to the ON state on detection of the WUS. Alternatively, a group of communication devices may be identified. By only waking up a group of communications devices, rather than all communications devices, to monitor a given WUS monitoring period, power consumption is reduced for those devices that are not part of the indicated group.

[0138] In some embodiments, each cyclically shifted data-carrying symbol is repeated to enhance coverage. When repeated, the communications device 101 combines all the repeated symbols before computing the cyclic shift applied to the repeated symbols. For example, each data- carrying symbol is repeated in the time domain. It will be appreciated that if there are N data- carrying symbols and each data-carrying symbol is repeated M times, then there are N / M potentially unique data-carrying symbols, each repeated M times, in order to create N data- carrying symbols in total.

[0139] Methods of receiving a WUS include:

[0140] • Time and frequency synchronisation

[0141] • Decoding of the data carried by the cyclic shift

[0142] Further details of receiving a WUS are described in [8], which is hereby incorporated by reference in its entirety.

[0143] Figure 12 is a flow diagram illustrating a method of operating a communications device to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment in accordance with example embodiments. The method starts in step S1.

[0144] Steps S2, S3 and S4 are performed while a low-power receiver of the communications device is in an ON state. A main receiver of the communications device may in the ON state or an OFF state during steps S2, S3 and S4. In step S2, the method comprises receiving, by the low-power receiver, one or more synchronisation signals (SSs) from the infrastructure equipment in one or more predefined SS reception periods.

[0145] In step S3, the method comprises synchronising the low-power receiver with the infrastructure equipment based on the one or more received SSs.

[0146] In particularly advantageous embodiments, step S4 is performed while the low-power receiver of the communications device is in the ON state and the main receiver of the communications device is in the OFF state.

[0147] In step S4, the method comprises monitoring, with the synchronised low-power receiver, one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment.

[0148] If the synchronised low-power receiver receives a WUS in one of the WUS monitoring periods, the method proceeds to step S5. If the synchronised low-power receiver does not receive a WUS in one of the WUS monitoring periods, the method returns to step S2

[0149] Step 5 is performed with a main receiver of the communications device in the ON state. The low power receiver may be in the ON or OFF state during step S5.

[0150] In step S5, the method comprises monitoring, with the main receiver, a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment. The downlink signal monitoring period is subsequent to the WUS monitoring period in which the WUS was received.

[0151] In particularly advantageous embodiments, where the low power receiver is in the ON state and the main receiver is in the OFF state in step S4, step S5 comprises transitioning the main receiver from the OFF state to the ON state to monitor the downlink signal monitoring period for reception of the downlink signal from the infrastructure equipment.

[0152] A power consumption of the low-power receiver when the low-power receiver is in the ON state is lower than a power consumption of the main receiver when the main receiver is in the ON state.

[0153] The method ends in step S7.

[0154] Figure 13 is a flow diagram illustrating a method of operating infrastructure equipment of a wireless communications network to communicate with one or more communications devices via a wireless radio interface provided by the infrastructure equipment in accordance with example embodiments. The one or more communications devices may be in an RRC-IDLE mode or RRC connected mode during the steps of Figure 13.

[0155] The method starts in step S11.

[0156] In step S12, the method comprises transmitting a Wake-Up signal (WUS) to at least one of the communications devices in a WUS transmission period. A WUS transmission period is a period during which the infrastructure equipment may transmit a WUS. In example embodiments according to Figure 13, the WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface. A first of the OFDM symbols is an identification symbol, and the OFDM symbols of the WUS subsequent to the identification symbol are data-carrying symbols. The OFDM symbols in the WUS are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence. The second sequence may be a Zadoff-Chu (ZC) sequence, for example. The one or more communications devices may monitor one or more WUS monitoring periods for the WUS. In particularly advantageous embodiments, the WUS may be used by the communications devices to transition their main receiver from the OFF state to the ON state to monitor a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment.

[0157] In step S13, the method comprises transmitting a downlink signal to the at least one communications device to which the WUS was transmitted in a downlink signal transmission period subsequent to the WUS transmission period.

[0158] In example embodiments according to Figure 13, the method may further comprise transmitting, to the one or more communications devices, one or more synchronisation signals (SSs) in one or more predefined SS transmission periods. An SS transmission period is a period during which an SS is transmitted by an infrastructure equipment of a wireless communications network and an SS reception period is a period during which an SS is received by a communications device. The one or more SSs may be used by the communications devices to synchronise their low-power receiver with the infrastructure equipment. In some embodiments, the at least one communications device which receives the WUS uses the WUS to synchronise its low-power receiver with the infrastructure equipment.

[0159] The method ends in step S14.

[0160] Those skilled in the art would further appreciate that such infrastructure equipment and / or communications devices as herein defined may be further defined in accordance with the various arrangements and embodiments discussed in the preceding paragraphs. It would be further appreciated by those skilled in the art that such infrastructure equipment and communications devices as herein defined and described may form part of communications systems other than those defined by the present disclosure.

[0161] Further examples of feature combinations taught by the present disclosure are set out in the following numbered paragraphs:

[0162] Paragraph 1. A method of operating a communications device to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment, the method comprising while a low-power receiver of the communications device is in an ON state, receiving, by the low-power receiver, one or more synchronisation signals (SSs) from the infrastructure equipment in one or more predefined SS reception periods, synchronising the low-power receiver with the infrastructure equipment based on the one or more received SSs, and monitoring, with the synchronised low-power receiver, one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment, and if the synchronised low-power receiver receives a WUS in one of the WUS monitoring periods, the method comprises while a main receiver of the communications device is in the ON state, monitoring, with the main receiver, a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment, the downlink signal monitoring period being subsequent to the WUS monitoring period in which the WUS was received, wherein a power consumption of the low-power receiver when the low-power receiver is in the ON state is lower than a power consumption of the main receiver when the main receiver is in the ON state.

[0163] Paragraph 2. A method according to paragraph 1 , wherein the monitoring, with the synchronised low-power receiver, of the one or more WUS monitoring periods for reception of a WUS from the infrastructure equipment is performed while the main receiver is in an OFF state, and the method comprises, if the synchronised low-power receiver receives a WUS in one of the WUS monitoring periods, transitioning the main receiver from the OFF state to the ON state to monitor the downlink signal monitoring period for reception of the downlink signal from the infrastructure equipment.

[0164] Paragraph 3. A method according to paragraph 1 or paragraph 2, wherein the one or more SSs are Primary Synchronisation Signals (PSSs) also used to synchronise the main receiver with the infrastructure equipment.

[0165] Paragraph 4. A method according to paragraph 1 or paragraph 2, wherein each of the one or more SSs is a random sequence comprised in a different Orthogonal Frequency Division Multiplexing (OFDM) symbol of the wireless radio interface.

[0166] Paragraph 5. A method according to any of paragraphs 1 to 4, wherein the receiving the one or more SSs in the one or more predefined SS reception periods comprises receiving a plurality of SSs in a respective plurality of predefined SS reception periods.

[0167] Paragraph 6. A method according to paragraph 5, wherein the receiving a plurality of SSs in a respective plurality of predefined SS reception periods comprises receiving the plurality of SSs in a respective plurality of predefined periodic SS reception periods.

[0168] Paragraph 7. A method according to any of paragraphs 1 to 6 wherein a bandwidth over which the low-power receiver is configured to receive signals from the infrastructure equipment is equal to or greater than a bandwidth of one or more synchronisation signal blocks, SSBs, transmitted by the infrastructure equipment to the communications device, and the method comprises, while the low-power receiver is in the ON state, receiving, by the low-power receiver, the one or more SSBs from the infrastructure equipment, and performing one or more RRM measurements on the one or more SSBs received from the infrastructure equipment.

[0169] Paragraph 8. A method according to paragraph 7, wherein the performing one or more RRM measurements on the one or more SSBs received from the infrastructure equipment comprises performing a reference signal received power (RSRP) measurement on the one or more SSBs received from the infrastructure equipment. Paragraph 9. A method according to paragraph 7 or paragraph 8, wherein the performing one or more RRM measurements on the one or more SSBs received from the infrastructure equipment comprises performing a reference signal received quality (RSRQ) measurement on the one or more SSBs received from the infrastructure equipment.

[0170] Paragraph 10. A method according to any of paragraphs 1 to 9, wherein the WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol, and the OFDM symbols of the WUS subsequent to the identification symbol are data-carrying symbols, wherein the OFDM symbols in the WUS are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence.

[0171] Paragraph 11 . A method according to paragraph 10, wherein the second sequence is a Zadoff-Chu (ZC) sequence.

[0172] Paragraph 12. A method according to paragraph 10 or paragraph 11 , wherein the identification symbol comprises an indication of a number of the data-carrying symbols in the WUS.

[0173] Paragraph 13. A method according to paragraph 12, wherein the number of the data-carrying symbols in the WUS is indicated by a time domain cyclic shift of the identification symbol.

[0174] Paragraph 14. A method according to any of paragraphs 11 to 13, wherein an index of the WUS monitoring period in which the WUS was received indicates the ZC sequence used for modulating the WUS.

[0175] Paragraph 15. A method according to any of paragraphs 10 to 14, wherein a subcarrier at a centre frequency of each of the plurality of OFDM symbols is not modulated.

[0176] Paragraph 16. A method according to any of paragraphs 10 to 15, wherein the data-carrying symbols in the WUS are cyclically shifted in time prior to transmission of the WUS by the infrastructure equipment, wherein the cyclic shift of each data-carrying symbol indicates data carried by that data-carrying symbol.

[0177] Paragraph 17. A method according to any of paragraphs 10 to 16, wherein data-carrying symbols in the WUS indicate a part of a cell ID of a cell provided by the infrastructure equipment in which the communications device is located and / or an identity of the communications device.

[0178] Paragraph 18. A method according to paragraph 17, wherein the one or more SSs are received by the main receiver when the main receiver is in the ON state, the one or more SSs are Primary Synchronisation signals, (PSSs), and the method comprises determining, from one of the PSSs received by the low-power receiver or the main receiver, another part of the cell ID, determining the cell ID based on the part of the cell ID indicated by the data-carrying symbols in the WUS and the other part of the cell ID determined from the PSS.

[0179] Paragraph 19. A method according to any of paragraphs 16 to 17, wherein each of the cyclically-shifted data-carrying symbols are repeated one or more times in the WUS, and the method comprises combining, for each data-carrying symbol in the WUS, the repetitions of that data- carrying symbol, and computing the cyclic shift applied to that data-carrying symbol.

[0180] Paragraph 20. A method of operating a communications device to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment, the method comprising while a low-power receiver of the communications device is in an ON state, monitoring, with a low-power receiver of the communications device, one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment, and if the low-power receiver receives a WUS in one of the WUS monitoring periods, the method comprises while a main receiver of the communications device is in the ON state, monitoring, with the main receiver, a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment, the downlink signal monitoring period being subsequent to the WUS monitoring period in which the WUS was received, wherein a power consumption of the low-power receiver when the low-power receiver is in the ON state is lower than a power consumption of the main receiver when the main receiver is in the ON state, and the received WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol and the OFDM symbols subsequent to the identification symbol are data- carrying symbols, wherein the data-carrying symbols are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence.

[0181] Paragraph 21. A method according to paragraph 20, wherein the monitoring, with the low- power receiver, of the one or more WUS monitoring periods for reception of a WUS from the infrastructure equipment is performed while the main receiver is in an OFF state, and the method comprises, if the synchronised low-power receiver receives a WUS in one of the WUS monitoring periods, transitioning the main receiver from the OFF state to the ON state to monitor the downlink signal monitoring period for reception of the downlink signal from the infrastructure equipment.

[0182] Paragraph 22. A method according to paragraph 20 or paragraph 21 , wherein the identification symbol is modulated by the sequence formed by the dot product of the PSS m-sequence and the second sequence.

[0183] Paragraph 23. A method according to any of paragraphs 20 to 22, wherein the second sequence is a Zadoff-Chu (ZC) sequence.

[0184] Paragraph 24. A method according to any of paragraphs 20 to 23, wherein the identification symbol comprises an indication of a number of the data-carrying symbols in the WUS.

[0185] Paragraph 25. A method according to paragraph 24, wherein the number of the data-carrying symbols in the WUS is indicated by a time domain cyclic shift of the identification symbol. Paragraph 26. A method according to any of paragraphs 20 to 25, wherein an index of the WUS monitoring period in which the WUS was received indicates the ZC sequence used for modulating the WUS.

[0186] Paragraph 27. A method according to any of paragraphs 20 to 26, wherein a subcarrier at a centre frequency of each of the plurality of OFDM symbols is not modulated.

[0187] Paragraph 28. A method according to any of paragraphs 20 to 27, wherein the data-carrying symbols in the WUS are cyclically shifted in time prior to transmission of the WUS by the infrastructure equipment, wherein the cyclic shift of each data-carrying symbol indicates data carried by that data-carrying symbol.

[0188] Paragraph 29. A method according to any of paragraphs 20 to 28, wherein data-carrying symbols in the WUS indicate a part of a cell ID of a cell provided by the infrastructure equipment in which the communications device is located and / or an identity of the communications device.

[0189] Paragraph 30. A method according to paragraph 29, wherein each of the cyclically-shifted data-carrying symbols are repeated one or more times in the WUS, and the method comprises combining, for each data-carrying symbol in the WUS, the repetitions of that data- carrying symbol, and computing the cyclic shift applied to that data-carrying symbol.

[0190] Paragraph 31 . A method according to any of paragraphs 20 to 30, comprising while the low power receiver is in the ON state, synchronising the low-power receiver with the infrastructure equipment based on the received WUS.

[0191] Paragraph 32. A method of operating infrastructure equipment of a wireless communications network to communicate with one or more communications devices via a wireless radio interface provided by the infrastructure equipment, the method comprising transmitting a Wake-Up signal (WUS) to at least one of the communications devices in a WUS transmission period, wherein the WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol, and the OFDM symbols of the WUS subsequent to the identification symbol are data- carrying symbols, wherein the OFDM symbols in the WUS are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence, and the method comprises transmitting a downlink signal to the at least one communications device to which the WUS was transmitted in a downlink signal transmission period subsequent to the WUS transmission period.

[0192] Paragraph 33. A method according to paragraph 32, wherein the second sequence is a Zadoff-Chu (ZC) sequence.

[0193] Paragraph 34. A method according to paragraph 32 or paragraph 33, wherein the identification symbol comprises an indication of a number of the data-carrying symbols in the WUS. Paragraph 35. A method according to paragraph 34 wherein the number of the data-carrying symbols in the WUS is indicated by a time domain cyclic shift of the identification symbol.

[0194] Paragraph 36. A method according to any of paragraphs 32 to 35, wherein an index of the WUS transmission period in which the WUS was transmitted indicates the ZC sequence used for modulating the WUS.

[0195] Paragraph 37. A method according to any of paragraphs 32 to 36, wherein a subcarrier at a centre frequency of each of the plurality of OFDM symbols is not modulated.

[0196] Paragraph 38. A method according to any of paragraphs 32 to 37, wherein the data-carrying symbols in the WUS are cyclically shifted in time prior to transmission of the WUS by the infrastructure equipment, wherein the cyclic shift of each data-carrying symbol indicates data carried by that data-carrying symbol.

[0197] Paragraph 39. A method according to any of paragraphs 32 to 38, wherein data-carrying symbols in the WUS indicate a part of a cell ID of a cell provided by the infrastructure equipment in which the communications device is located and / or an identity of the communications device.

[0198] Paragraph 40. A method according to any of paragraphs 32 to 39, comprising transmitting, to the one or more communications devices, one or more synchronisation signals (SSs) in one or more predefined SS transmission periods.

[0199] Paragraph 41 . A communications device operable to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment, the communications device comprising a transmitter configured to transmit signals, a low-power receiver configured to receive signals, a main receiver configured to receive signals, and at least one controller configured to control the transmitter, the low-power receiver and the main receiver, wherein the at least one controller is configured to control the low-power receiver to while the low-power receiver of the communications device is in an ON state, receive one or more synchronisation signals (SSs) from the infrastructure equipment in one or more predefined SS reception periods, synchronise with the infrastructure equipment based on the one or more received SSs, and monitor one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment, and if the low-power receiver receives a WUS in one of the WUS monitoring periods, the at least one controller is configured to control the main receiver to while the main receiver of the communications device is in the ON state, monitor a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment, the downlink signal monitoring period being subsequent to the WUS monitoring period in which the WUS was received, wherein a power consumption of the low-power receiver when the low-power receiver is in the ON state is lower than a power consumption of the main receiver when the main receiver is in the ON state.

[0200] Paragraph 42. A communications device operable to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment, the communications device comprising a transmitter configured to transmit signals, a low-power receiver configured to receive signals, a main receiver configured to receive signals, and at least one controller configured to control the transmitter, the low-power receiver and the main receiver, wherein the at least one controller is configured to control the low-power receiver to while the low-power receiver of the communications device is in an ON state, monitoring one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment, and if the low-power receiver receives a WUS in one of the WUS monitoring periods, the at least one controller is configured to control the main receiver to while the main receiver of the communications device is in the ON state, monitor a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment, the downlink signal monitoring period being subsequent to the WUS monitoring period in which the WUS was received, wherein a power consumption of the low-power receiver when the low-power receiver is in the ON state is lower than a power consumption of the main receiver when the main receiver is in the ON state, and the received WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol and the OFDM symbols subsequent to the identification symbol are data- carrying symbols, wherein the data-carrying symbols are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence.

[0201] Paragraph 43. Infrastructure equipment of a wireless communications network operable to communicate with one or more communications devices via a wireless radio interface provided by the infrastructure equipment, the infrastructure equipment comprising a transceiver configured to transmit and receive signals, a controller configured to control the transceiver to transmit a Wake-Up signal (WUS) to at least one of the communications devices in a WUS transmission period, wherein the WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol, and the OFDM symbols of the WUS subsequent to the identification symbol are data- carrying symbols, wherein the OFDM symbols in the WUS are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence, wherein the controller configured to control the transceiver to transmit a downlink signal to the at least one communications device to which the WUS was transmitted in a downlink signal transmission period subsequent to the WUS transmission period.

[0202] Paragraph 44. Circuitry for a communications device operable to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment, the circuitry comprising transmitter circuitry configured to transmit signals, low-power receiver circuitry configured to receive signals, main receiver circuitry configured to receive signals, and controller circuitry configured to control the transmitter circuitry, the low-power receiver circuitry and the main receiver circuitry, wherein the controller circuitry is configured to control the low-power receiver circuitry to while the low-power receiver circuitry of the communications device is in an ON state, receive one or more synchronisation signals (SSs) from the infrastructure equipment in one or more predefined SS reception periods, synchronise with the infrastructure equipment based on the one or more received SSs, and monitor one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment, and if the low-power receiver circuitry receives a WUS in one of the WUS monitoring periods, the controller circuitry is configured to control the main receiver circuitry to while the main receiver circuitry of the communications device is in the ON state, monitor a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment, the downlink signal monitoring period being subsequent to the WUS monitoring period in which the WUS was received, wherein a power consumption of the low-power receiver circuitry when the low-power receiver circuitry is in the ON state is lower than a power consumption of the main receiver circuitry when the main receiver circuitry is in the ON state.

[0203] Paragraph 45. Circuitry for a communications device operable to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment, the circuitry comprising transmitter circuitry configured to transmit signals, low-power receiver circuitry configured to receive signals, main receiver circuitry configured to receive signals, and controller circuitry configured to control the transmitter circuitry, the low-power receiver circuitry and the main receiver circuitry, wherein the controller circuitry is configured to control the low-power receiver circuitry to while the low-power receiver circuitry of the communications device is in an ON state, monitoring one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment, and if the low-power receiver circuitry receives a WUS in one of the WUS monitoring periods, the controller circuitry is configured to control the main receiver circuitry to while the main receiver circuitry of the communications device is in the ON state, monitor a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment, the downlink signal monitoring period being subsequent to the WUS monitoring period in which the WUS was received, wherein a power consumption of the low-power receiver circuitry when the low-power receiver circuitry is in the ON state is lower than a power consumption of the main receiver circuitry when the main receiver circuitry is in the ON state, and the received WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol and the OFDM symbols subsequent to the identification symbol are data- carrying symbols, wherein the data-carrying symbols are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence.

[0204] Paragraph 46. Circuitry for infrastructure equipment of a wireless communications network operable to communicate with one or more communications devices via a wireless radio interface provided by the infrastructure equipment, the circuitry comprising transceiver circuitry configured to transmit and receive signals, controller circuitry configured to control the transceiver to transmit a Wake-Up signal (WUS) to at least one of the communications devices in a WUS transmission period, wherein the WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol, and the OFDM symbols of the WUS subsequent to the identification symbol are data- carrying symbols, wherein the OFDM symbols in the WUS are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence, wherein the controller configured to control the transceiver to transmit a downlink signal to the at least one communications device to which the WUS was transmitted in a downlink signal transmission period subsequent to the WUS transmission period.

[0205] Paragraph 47. A wireless communications network comprising a communications device according to paragraph 41 or paragraph 42 and infrastructure equipment according to paragraph 43.

[0206] Paragraph 48. A computer program which, when the program is executed by a computer, cause the computer to perform the method of any of paragraphs 1 to 40.

[0207] Paragraph 49. A non-transitory computer-readable storage medium storing a computer program according to paragraph 48. It will be appreciated that the above description for clarity has described embodiments with reference to different functional units, circuitry and / or processors. However, it will be apparent that any suitable distribution of functionality between different functional units, circuitry and / or processors may be used without detracting from the embodiments.

[0208] Described embodiments may be implemented in any suitable form including hardware, software, firmware or any combination of these. Described embodiments may optionally be implemented at least partly as computer software running on one or more data processors and / or digital signal processors. The elements and components of any embodiment may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the disclosed embodiments may be implemented in a single unit or may be physically and functionally distributed between different units, circuitry and / or processors.

[0209] Although the present disclosure has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in any manner suitable to implement the technique.

[0210] REFERENCES

[0211] [1] Holma H. and Toskala A, “LTE for UMTS OFDMA and SC-FDMA based radio access”, John Wiley and Sons, 2009.

[0212] [2] TR 38.913, “3rdGeneration Partnership Project; Technical Specification Group Radio Access Network; Study on Scenarios and Requirements for Next Generation Access Technologies (Release 14)”, 3GPP, v14.3.0, August 2017.

[0213] [3] R1-1708311 , “Idle Mode Power Efficiency Reduction,” Sierra Wireless, RAN1#89.

[0214] [4] TS 38.213, “Physical layer procedures for control (Release 18)”, 3GPP, v18.1.0, December 2023.

[0215] [5] TR 38.840, “NR: Study on UE Power Saving (Release 16, vO.1.0)”, 3GPP, November 2018.

[0216] [6] RP-222644, “Revised SID: Study on low-power Wake-up Signal and Receiver for NR”, RANP#97e, September 2022.

[0217] [7] European Patent Application Number EP23185615.4.

[0218] [8] PCT Patent Application with Publication Number WO 2019030337.

Claims

CLAIMS1. A method of operating a communications device to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment, the method comprising while a low-power receiver of the communications device is in an ON state, receiving, by the low-power receiver, one or more synchronisation signals (SSs) from the infrastructure equipment in one or more predefined SS reception periods, synchronising the low-power receiver with the infrastructure equipment based on the one or more received SSs, and monitoring, with the synchronised low-power receiver, one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment, and if the synchronised low-power receiver receives a WUS in one of the WUS monitoring periods, the method comprises while a main receiver of the communications device is in the ON state, monitoring, with the main receiver, a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment, the downlink signal monitoring period being subsequent to the WUS monitoring period in which the WUS was received, wherein a power consumption of the low-power receiver when the low-power receiver is in the ON state is lower than a power consumption of the main receiver when the main receiver is in the ON state.

2. A method according to claim 1 , wherein the monitoring, with the synchronised low- power receiver, of the one or more WUS monitoring periods for reception of a WUS from the infrastructure equipment is performed while the main receiver is in an OFF state, and the method comprises, if the synchronised low-power receiver receives a WUS in one of the WUS monitoring periods, transitioning the main receiver from the OFF state to the ON state to monitor the downlink signal monitoring period for reception of the downlink signal from the infrastructure equipment.

3. A method according to claim 1 , wherein the one or more SSs are Primary Synchronisation Signals (PSSs) also used to synchronise the main receiver with the infrastructure equipment.

4. A method according to claim 1 , wherein each of the one or more SSs is a random sequence comprised in a different Orthogonal Frequency Division Multiplexing (OFDM) symbol of the wireless radio interface.

5. A method according to claim 1 , wherein the receiving the one or more SSs in the one or more predefined SS reception periods comprises receiving a plurality of SSs in a respective plurality of predefined SS reception periods.

6. A method according to claim 5, wherein the receiving a plurality of SSs in a respective plurality of predefined SS reception periods comprises receiving the plurality of SSs in a respective plurality of predefined periodic SS reception periods.

7. A method according to claim 1 , wherein a bandwidth over which the low-power receiver is configured to receive signals from the infrastructure equipment is equal to or greater than a bandwidth of one or more synchronisation signal blocks, SSBs, transmitted by the infrastructure equipment to the communications device, and the method comprises, while the low-power receiver is in the ON state, receiving, by the low-power receiver, the one or more SSBs from the infrastructure equipment, and performing one or more RRM measurements on the one or more SSBs received from the infrastructure equipment.

8. A method according to claim 7, wherein the performing one or more RRM measurements on the one or more SSBs received from the infrastructure equipment comprises performing a reference signal received power (RSRP) measurement on the one or more SSBs received from the infrastructure equipment.

9. A method according to claim 7, wherein the performing one or more RRM measurements on the one or more SSBs received from the infrastructure equipment comprises performing a reference signal received quality (RSRQ) measurement on the one or more SSBs received from the infrastructure equipment.

10. A method according to claim 1, wherein the WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol, and the OFDM symbols of the WUS subsequent to the identification symbol are data-carrying symbols, wherein the OFDM symbols in the WUS are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence.

11. A method according to claim 10, wherein the second sequence is a Zadoff-Chu (ZC) sequence.

12. A method according to claim 10, wherein the identification symbol comprises an indication of a number of the data-carrying symbols in the WUS.

13. A method according to claim 12, wherein the number of the data-carrying symbols in the WUS is indicated by a time domain cyclic shift of the identification symbol.

14. A method according to claim 11 , wherein an index of the WUS monitoring period in which the WUS was received indicates the ZC sequence used for modulating the WUS.

15. A method according to claim 10, wherein a subcarrier at a centre frequency of each of the plurality of OFDM symbols is not modulated.

16. A method according to claim 10, wherein the data-carrying symbols in the WUS are cyclically shifted in time prior to transmission of the WUS by the infrastructure equipment, wherein the cyclic shift of each data-carrying symbol indicates data carried by that data- carrying symbol.

17. A method according to claim 10, wherein data-carrying symbols in the WUS indicate a part of a cell ID of a cell provided by the infrastructure equipment in which the communications device is located and / or an identity of the communications device.

18. A method according to claim 17, wherein the one or more SSs are received by the main receiver when the main receiver is in the ON state, the one or more SSs are Primary Synchronisation signals, (PSSs), and the method comprises determining, from one of the PSSs received by the low-power receiver or the main receiver, another part of the cell ID, determining the cell ID based on the part of the cell ID indicated by the data-carrying symbols in the WUS and the other part of the cell ID determined from the PSS.

19. A method according to claim 16, wherein each of the cyclically-shifted data-carrying symbols are repeated one or more times in the WUS, and the method comprises combining, for each data-carrying symbol in the WUS, the repetitions of that data- carrying symbol, and computing the cyclic shift applied to that data-carrying symbol.

20. A method of operating a communications device to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment, the method comprising while a low-power receiver of the communications device is in an ON state, monitoring, with a low-power receiver of the communications device, one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment, and if the low-power receiver receives a WUS in one of the WUS monitoring periods, the method comprises while a main receiver of the communications device is in the ON state, monitoring, with the main receiver, a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment, the downlink signal monitoring period being subsequent to the WUS monitoring period in which the WUS was received, wherein a power consumption of the low-power receiver when the low-power receiver is in the ON state is lower than a power consumption of the main receiver when the main receiver is in the ON state, and the received WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol and the OFDM symbols subsequent to the identification symbol are data- carrying symbols, wherein the data-carrying symbols are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence.21 . A method according to claim 20, wherein the monitoring, with the low-power receiver, of the one or more WUS monitoring periods for reception of a WUS from the infrastructure equipment is performed while the main receiver is in an OFF state, and the method comprises, if the synchronised low-power receiver receives a WUS in one of the WUS monitoring periods, transitioning the main receiver from the OFF state to the ON state to monitor the downlink signal monitoring period for reception of the downlink signal from the infrastructure equipment.

22. A method according to claim 20, wherein the identification symbol is modulated by the sequence formed by the dot product of the PSS m-sequence and the second sequence.

23. A method according to claim 20, wherein the second sequence is a Zadoff-Chu (ZC) sequence.

24. A method according to claim 20, wherein the identification symbol comprises an indication of a number of the data-carrying symbols in the WUS.

25. A method according to claim 24, wherein the number of the data-carrying symbols in the WUS is indicated by a time domain cyclic shift of the identification symbol.

26. A method according to claim 20, wherein an index of the WUS monitoring period in which the WUS was received indicates the ZC sequence used for modulating the WUS.

27. A method according to claim 20, wherein a subcarrier at a centre frequency of each of the plurality of OFDM symbols is not modulated.

28. A method according to claim 20, wherein the data-carrying symbols in the WUS are cyclically shifted in time prior to transmission of the WUS by the infrastructure equipment, wherein the cyclic shift of each data-carrying symbol indicates data carried by that data- carrying symbol.

29. A method according to claim 20, wherein data-carrying symbols in the WUS indicate a part of a cell ID of a cell provided by the infrastructure equipment in which the communications device is located and / or an identity of the communications device.

30. A method according to claim 29, wherein each of the cyclically-shifted data-carrying symbols are repeated one or more times in the WUS, and the method comprises combining, for each data-carrying symbol in the WUS, the repetitions of that data- carrying symbol, and computing the cyclic shift applied to that data-carrying symbol.31 . A method according to claim 20, comprising while the low power receiver is in the ON state, synchronising the low-power receiver with the infrastructure equipment based on the received WUS.

32. A method of operating infrastructure equipment of a wireless communications network to communicate with one or more communications devices via a wireless radio interface provided by the infrastructure equipment, the method comprising transmitting a Wake-Up signal (WUS) to at least one of the communications devices in a WUS transmission period, wherein the WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol, and the OFDM symbols of the WUS subsequent to the identification symbol are data- carrying symbols, wherein the OFDM symbols in the WUS are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence, and the method comprisestransmitting a downlink signal to the at least one communications device to which the WUS was transmitted in a downlink signal transmission period subsequent to the WUS transmission period.

33. A method according to claim 32, wherein the second sequence is a Zadoff-Chu (ZC) sequence.

34. A method according to claim 32, wherein the identification symbol comprises an indication of a number of the data-carrying symbols in the WUS.

35. A method according to claim 34 wherein the number of the data-carrying symbols in the WUS is indicated by a time domain cyclic shift of the identification symbol.

36. A method according to claim 32, wherein an index of the WUS transmission period in which the WUS was transmitted indicates the ZC sequence used for modulating the WUS.

37. A method according to claim 32, wherein a subcarrier at a centre frequency of each of the plurality of OFDM symbols is not modulated.

38. A method according to claim 32, wherein the data-carrying symbols in the WUS are cyclically shifted in time prior to transmission of the WUS by the infrastructure equipment, wherein the cyclic shift of each data-carrying symbol indicates data carried by that data- carrying symbol.

39. A method according to claim 32, wherein data-carrying symbols in the WUS indicate a part of a cell ID of a cell provided by the infrastructure equipment in which the communications device is located and / or an identity of the communications device.

40. A method according to claim 32, comprising transmitting, to the one or more communications devices, one or more synchronisation signals (SSs) in one or more predefined SS transmission periods.41 . A communications device operable to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment, the communications device comprising a transmitter configured to transmit signals, a low-power receiver configured to receive signals, a main receiver configured to receive signals, andat least one controller configured to control the transmitter, the low-power receiver and the main receiver, wherein the at least one controller is configured to control the low-power receiver to while the low-power receiver of the communications device is in an ON state, receive one or more synchronisation signals (SSs) from the infrastructure equipment in one or more predefined SS reception periods, synchronise with the infrastructure equipment based on the one or more received SSs, and monitor one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment, and if the low-power receiver receives a WUS in one of the WUS monitoring periods, the at least one controller is configured to control the main receiver to while the main receiver of the communications device is in the ON state, monitor a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment, the downlink signal monitoring period being subsequent to the WUS monitoring period in which the WUS was received, wherein a power consumption of the low-power receiver when the low-power receiver is in the ON state is lower than a power consumption of the main receiver when the main receiver is in the ON state.

42. A communications device operable to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment, the communications device comprising a transmitter configured to transmit signals, a low-power receiver configured to receive signals, a main receiver configured to receive signals, and at least one controller configured to control the transmitter, the low-power receiver and the main receiver, wherein the at least one controller is configured to control the low-power receiver to while the low-power receiver of the communications device is in an ON state, monitoring one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment, and if the low-power receiver receives a WUS in one of the WUS monitoring periods, the at least one controller is configured to control the main receiver to while the main receiver of the communications device is in the ON state, monitor a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment, the downlink signal monitoring period being subsequent to the WUS monitoring period in which the WUS was received, whereina power consumption of the low-power receiver when the low-power receiver is in the ON state is lower than a power consumption of the main receiver when the main receiver is in the ON state, and the received WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol and the OFDM symbols subsequent to the identification symbol are data- carrying symbols, wherein the data-carrying symbols are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence.

43. Infrastructure equipment of a wireless communications network operable to communicate with one or more communications devices via a wireless radio interface provided by the infrastructure equipment, the infrastructure equipment comprising a transceiver configured to transmit and receive signals, a controller configured to control the transceiver to transmit a Wake-Up signal (WUS) to at least one of the communications devices in a WUS transmission period, wherein the WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol, and the OFDM symbols of the WUS subsequent to the identification symbol are data- carrying symbols, wherein the OFDM symbols in the WUS are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence, wherein the controller configured to control the transceiver to transmit a downlink signal to the at least one communications device to which the WUS was transmitted in a downlink signal transmission period subsequent to the WUS transmission period.

44. Circuitry for a communications device operable to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment, the circuitry comprising transmitter circuitry configured to transmit signals, low-power receiver circuitry configured to receive signals, main receiver circuitry configured to receive signals, and controller circuitry configured to control the transmitter circuitry, the low-power receiver circuitry and the main receiver circuitry, wherein the controller circuitry is configured to control the low-power receiver circuitry to while the low-power receiver circuitry of the communications device is in an ON state, receive one or more synchronisation signals (SSs) from the infrastructure equipment in one or more predefined SS reception periods, synchronise with the infrastructure equipment based on the one or more received SSs, andmonitor one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment, and if the low-power receiver circuitry receives a WUS in one of the WUS monitoring periods, the controller circuitry is configured to control the main receiver circuitry to while the main receiver circuitry of the communications device is in the ON state, monitor a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment, the downlink signal monitoring period being subsequent to the WUS monitoring period in which the WUS was received, wherein a power consumption of the low-power receiver circuitry when the low-power receiver circuitry is in the ON state is lower than a power consumption of the main receiver circuitry when the main receiver circuitry is in the ON state.

45. Circuitry for a communications device operable to communicate with infrastructure equipment of a wireless communications network via a wireless radio interface provided by the infrastructure equipment, the circuitry comprising transmitter circuitry configured to transmit signals, low-power receiver circuitry configured to receive signals, main receiver circuitry configured to receive signals, and controller circuitry configured to control the transmitter circuitry, the low-power receiver circuitry and the main receiver circuitry, wherein the controller circuitry is configured to control the low-power receiver circuitry to while the low-power receiver circuitry of the communications device is in an ON state, monitoring one or more Wake-Up Signal (WUS) monitoring periods for reception of a WUS from the infrastructure equipment, and if the low-power receiver circuitry receives a WUS in one of the WUS monitoring periods, the controller circuitry is configured to control the main receiver circuitry to while the main receiver circuitry of the communications device is in the ON state, monitor a downlink signal monitoring period for reception of a downlink signal from the infrastructure equipment, the downlink signal monitoring period being subsequent to the WUS monitoring period in which the WUS was received, wherein a power consumption of the low-power receiver circuitry when the low-power receiver circuitry is in the ON state is lower than a power consumption of the main receiver circuitry when the main receiver circuitry is in the ON state, and the received WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol and the OFDM symbols subsequent to the identification symbol are data- carrying symbols, wherein the data-carrying symbols are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence.

46. Circuitry for infrastructure equipment of a wireless communications network operable to communicate with one or more communications devices via a wireless radio interface provided by the infrastructure equipment, the circuitry comprising transceiver circuitry configured to transmit and receive signals, controller circuitry configured to control the transceiver to transmit a Wake-Up signal (WUS) to at least one of the communications devices in a WUS transmission period, wherein the WUS comprises a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols of the wireless radio interface, a first of the OFDM symbols being an identification symbol, and the OFDM symbols of the WUS subsequent to the identification symbol are data- carrying symbols, wherein the OFDM symbols in the WUS are modulated by a sequence formed by a dot product of a Primary Synchronisation Signal (PSS) m-sequence and a second sequence, wherein the controller configured to control the transceiver to transmit a downlink signal to the at least one communications device to which the WUS was transmitted in a downlink signal transmission period subsequent to the WUS transmission period.

47. A wireless communications network comprising a communications device according to claim 41 or claim 42 and infrastructure equipment according to claim 43.

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

49. A non-transitory computer-readable storage medium storing a computer program according to claim 48.

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