Reader to device on off keying (OOK) signal

Abstract

Methods, reader devices, communications devices, and circuitry are provided for providing a R2D signal that is compatible with legacy OFDM-based systems, where the R2D signal includes a data portion of reduced length, a cyclic prefix (CP), and a tail portions, where the CP is a duplicate of the tail portion. The CP and tail portion may be predetermined signals, or may be used to carry information, for example information based on data within the data portion, or standalone data.

Description

[0001] READER TO DEVICE ON OFF KEYING (OOK) SIGNAL

[0002] The present application claims the Paris Convention priority of European patent application EP24192725.0, filed 2 August 2024, the contents of which are hereby incorporated by reference.

[0003] BACKGROUND

[0004] Field of the Disclosure

[0005] The present disclosure relates to methods, a communications device and infrastructure equipment of a wireless communications network.

[0006] Background

[0007] The “background” description provided 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 the 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 disclosure.

[0008] Recent generation mobile telecommunication systems, such as those based on the 3rdGeneration Partnership Project (3GPP (RTM)) defined Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE) and 5G New Radio (NR) architectures, are able to support a wider range of services than simple voice and messaging services offered by previous generations of mobile telecommunication systems. For example, with the improved radio interface and enhanced data rates provided by LTE and NR systems, a user is able to experience high data rate applications such as mobile video streaming and mobile video conferencing that would previously only have been available via a fixed line data connection. In addition to supporting these kinds of more sophisticated services and devices, it is also proposed for newer generation mobile telecommunication systems such as NR to support less complex services and devices which make use of the reliable and wide ranging coverage of newer generation mobile telecommunication systems without necessarily needing to rely on the high data rates available in such systems. For example, a less complex device (such as an Internet-of-Things (loT) device) may be a tiny device equipped with sensors and a small battery capacity. Such a less complex device needs to transmit the sensor data at a typically infrequent and / or low data rate. Furthermore some devices (such as ambient loT devices) may not include a power source and may derive power for transmitting signals based on a received radio frequency carrier wave.

[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 loT devices, ambient loT 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 loT devices, 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

[0010] 1 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).

[0011] 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. 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

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

[0014] Respective aspects and features of the present disclosure are defined in the appended claims.

[0015] 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.

[0016] BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Non-limiting embodiments and advantages of the present disclosure are explained with reference to the following detailed description taken in conjunction with the accompanying drawings, in which like parts have the same numerical designations and wherein:

[0018] Figures 1A and 1 B schematically represent examples of communication systems in which tags are deployed within a coverage area of an infrastructure equipment (e.g. a gNB) of a wireless communications network and in which carrier wave emitters are controlled by the infrastructure equipment to transmit carrier wave signals and backscattered signals are detected;

[0019] Figure 2 is a schematic block diagram illustrating an example wireless communications network configured in accordance with a 5G or new radio (NR) 3GPP standard according to example embodiments;

[0020] Figure 3 is a schematic block diagram illustrating in more detail a communications device (e.g. a UE) and an infrastructure equipment (e.g. a gNB) formed from components of the wireless communications network shown in Figure 2;

[0021] Figure 4 is a schematic block diagram illustrating an example of backscattering circuitry;

[0022] Figure 5 is a schematic illustration representing an example in which a carrier wave signal transmitted by an external carrier wave emitter is backscattered; Figure 6 schematically illustrates an example of an ambient loT device communicating with a network;

[0023] Figure 7 illustrates examples of a reader (i.e. reader device) according to the present disclosure;

[0024] Figure 8 illustrates a layout of an R2D signal according to the present disclosure;

[0025] Figure 9 illustrates a method of generating a time-domain R2D signal superposed with an NR signal;

[0026] Figure 10 illustrates an example R2D signal structure according to an example of the present disclosure;

[0027] Figure 11 illustrates an R2D signal where a CP and tail portion is an ON signal according to an example of the present disclosure;

[0028] Figure 12 illustrates an R2D signal where a CP and tail portion is an OFF signal according to an example of the present disclosure;

[0029] Figure 13 illustrates an R2D signal where a CP and tail portion is an ON-OFF signal according to an example of the present disclosure;

[0030] Figure 14 illustrates an R2D signal where a CP and tail portion is an OFF-ON signal according to an example of the present disclosure;

[0031] Figure 15 illustrates an R2D signal where a structure of a CP and tail portion is based on data to be inferred from the CP and tail portion, according to an example of the present disclosure;

[0032] Figure 16 illustrates an R2D signal where a CP and tail portion is repeated across multiple OFDM symbols, according to an example of the present disclosure;

[0033] Figure 17 illustrates an R2D signal where a structure of a CP and tail portion is based on data carried by a data portion of the R2D signal, according to an example of the present disclosure;

[0034] Figure 18 illustrates an R2D signal where a CP and tail portion is an early extension of the data portion;

[0035] Figure 19 illustrates an R2D signal where a CP and tail portion is a late extension of the data portion;

[0036] Figure 20 illustrates an R2D signal where the CP and tail portion is contiguous across multiple OFDM symbols;

[0037] Figure 21 illustrates an R2D signal where a CP and tail portion have a greater amplitude than a data portion of the R2D signal;

[0038] Figure 22 illustrates a flowchart for a method for a reader device according to an example of the present disclosure.

[0039] Figure 23 illustrates a flowchart for a method for a communications device according to an example of the present disclosure.

[0040] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] Ambient loT In release 19 of 3GPP (Rel-19), 3GPP will study Ambient loT [1] where a communications device (such as a user equipment (UE)) is essentially a zero power communications device. In Ambient loT, it is considered that the communications device can harvest energy to power its communication with a base station (such as a gNB). For example, the energy can be harvested from solar or kinetic energy such as vibrations. Alternatively, the energy to power the communications device can come from incident radio frequency (RF) energy, either directly from a base station or from a carrier wave emitter (CWE). An example in which such communication devices are powered by radio frequency energy derived from radio signals transmitted as a carrier wave (CW) by a CWE is shown in Figures 1 A and 1 B. Figures 1 A and 1 B show a plurality of low- complexity communications devices 1 , which can be deployed in accordance with an ambient loT scenario, which can be referred to as “tags” because of the simplicity of the devices. These tags 1 are powered as a result of radio frequency energy received from an incident CW 2 transmitted by the CWE 3.

[0042] In a first example illustrated by Figure 1A, a base station 4, or gNB 4 according to 3GPP 5G terminology, receives a backscattered signal 5 from the tags 1 , the backscattered signal 5 being formed as a reflection of the carrier wave 2 transmitted by the CWE 3.

[0043] In a second example, a UE 7 receives a backscattered signal 5 from the tags 1. The UE 7 then transmits an indication of the received backscattered signals 5, which were received from the tags 1 , to the gNB 4 via a wireless access interface 8 formed between the gNB 4 and the UE 7. Therefore, the gNB 4 may control the CWEs 3 to transmit the CWs 2, and the backscattered signals are detected by the detection station (UE) 7, and the detection station transmits an indication of the detected backscattered signals to the gNB 4.

[0044] The station which controls the CWEs 3 may be regarded as a controller station. The station which detects the backscattered signals 5 may be regarded as detection station. The detection station may also be referred to as reader. Therefore in the Figure 1A both the controller station and the detection station are formed by a gNB 4 whereas in Figure 1 B the detection station 7 in the form of the UE is separate from the gNB 4 which acts as a controller station.

[0045] According to the arrangements of Figures 1A and 1 B, the tags 1 may modulate the reflected or backscattered signal 5 with information which is detected by the gNB 4 or a UE 7 acting as a detection station.

[0046] As shown in Figures 1A and 1 B, the gNB 4, which provides a cell represented by dashed line 12 controls the CWE 3 to transmit the CW 2. In some examples, the CWE 3 is formed by a communications device (such as a UE) which operates with a wireless communications network of which the gNB 4 forms part. The gNB 4 has an interface 6 to the CWE 3. In some examples therefore the interface 6 may be a Uu interface using 3GPP terminology. In some examples, the CWE is part of the gNB 4. In this case, the interface 6 can be an internal interface to the gNB 4.

[0047] The CWE 3 can be a standalone device or can be part of another network node. In one example, the CWE is a UE, such as a legacy UE or smartphone. In this case, the UE can be controlled to send a suitable signal to act as a carrier wave signal. It is also possible for the AloT device to transmit data in the uplink by backscattering another signal (for example the DL signal from the gNB 4).

[0048] In some examples, such as the example of Figure 1 B, the backscattered signal 5 may be received by a separate detection station (e.g. UE 7) which does not form part of the gNB 4. However since example embodiments can operate within or in association with wireless communications networks, an architecture of a typical 5G or New Radio (NR) wireless communications network will be now be described with reference to Figures 2 and 3.

[0049] In some examples the CWE 3 may be incorporated within the detection station as a reader, in that the reader both emits the carrier wave signals and detects the backscattered signal from the one or more tags. The reader may then send the decoded information to the controller station.

[0050] 5G New Radio (NR) Wireless Communications System

[0051] Systems incorporating NR technology 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].

[0052] 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 (I loT) in order to support services with new requirements of high availability, high reliability, low latency, and in some cases, high-accuracy positioning.

[0053] An example configuration of a wireless communications network which uses some of the terminology proposed for NR is shown in Figure 2. In Figure 2 a plurality of transmission and reception points (TRPs) 10 are connected to distributed control units (DUs) 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 dashed line 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 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 a core network 20 which may contain all other functions required for communicating data to and from the wireless communications devices and the core network 20. The core network 20 may be connected to other radio networks and infrastructure equipment.

[0054] The elements of the wireless access network shown in Figure 2 may operate in a similar way to corresponding elements of an LTE network. 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.

[0055] The TRPs 10 of Figure 2 may in part have a corresponding functionality to a base station or eNodeB of an LTE network. It will be appreciated, therefore, that operational aspects of an NR 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 an NR network will be functionally similar to, respectively, the core network component, base stations and communications devices of an LTE wireless communications network. 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. As such, the terms infrastructure equipment, base station, transceiver stations, nodeBs, e-nodeBs, eNB, g-nodeBs, and gNB are used interchangeably in the present disclosure.

[0056] The term network infrastructure equipment I access node may be used to encompass the central unit 40 and associated DU 42 and TRP 10 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 CU 40, DUs 42 and / or TRPs 10. Communications devices 14 are represented in Figure 2 within the coverage area of respective communication cells 12. These communications devices 14 may thus exchange signalling with the CU 40 via the TRP 10 associated with their respective communications cells 12.

[0057] It will further be appreciated that Figure 2 represents merely one example of a proposed architecture for an NR-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.

[0058] 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 is configured to control the transmitter 30 and the receiver 32 to transmit radio signals to and receive radio signals from 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 wireless transmitter 49, wireless receiver 48 and a controller or controlling processor 44 which is configured to control the transmitter 49 to transmit signals representing uplink data to the wireless communications network via the wireless access interface formed by the TRP 10 and the receiver 48 to receive downlink data as signals transmitted by the transmitter 30 in accordance with the conventional operation.

[0059] 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.

[0060] 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, for example, may be formed from a fibre optic or other wired high bandwidth connection. In one example, the connection 16 from the TRP 10 to the DU 42 is via fibre optic. The connection between a TRP 10 and the core network 20 can be generally referred to as a backhaul, which comprises the interface 16 from TRP10 to the DU 42 and the F1 interface 46 from the DU 42 to the CU 40.

[0061] RF Incident Energy

[0062] As explained above with reference to the example shown in Figure 1 , Ambient loT proposes to use energy received from a radio frequency carrier wave in order to power devices. An Ambient loT device could be powered by other ambient power sources, such as solar or thermal power. Harvesting energy based on the incident RF energy has several advantages and disadvantages.

[0063] An advantage is the RF energy is always available. Hence the Ambient loT device can always be awake while being powered from this energy. Furthermore a signal transmitted in the uplink from a tag can be backscattered using the incident radio frequency wave.

[0064] A disadvantage is the received power of the RF energy source is typically low. A receiver operating on such energy typically requires a power level of -30dBm to -20dBm for operation, which is not consistent with the low amounts of received power that are typically available directly from a base station. This required received power level sets a limit on the range (communication distance) supported by the AloT system.

[0065] Another disadvantage is the transmission power level of a device that is powered by an RF energy source is typically very low. Such devices may operate based on backscattering technology, for example. The backscattered signal is created at the same carrier frequency as the incident RF energy. It is thus hard for the source of the RF energy (e.g. a gNB) to differentiate between the transmitted RF signal and the backscattered signal.

[0066] Another disadvantage is that, to reduce the power consumption of a receiver that operates on incident RF energy, a low power waveform I signaling scheme that is amenable to being decoded and received by a low power consumption receiver is typically required. For example, an on-off keying (OOK) signaling scheme may be used for such lower power communications. There are then issues of multiplexing this new signaling scheme with the currently supported orthogonal frequency-division multiplexing (OFDM) and Discrete Fourier Transform-spread (DFT-s)-OFDM waveforms.

[0067] Despite the above listed disadvantages, it is considered that Ambient loT based on RF incident energy is feasible. Hence, 3GPP have started a study item on Ambient loT technology [1] and collected some initial design targets, requirements, topologies, deployment scenarios, etc., in a technical report TR38.848 [3],

[0068] Backscattering Principle

[0069] A passive device can transmit in the uplink (UL) using the backscattering principle. The UL signal can be backscattered on RF incident energy that can be either ambient (some RF energy that is already being transmitted in the ether, such as a cellular radio signal or a TV signal) or transmitted as a carrier-wave by a CW emitter for the express purpose of being backscattered. In either case, backscattering is performed based on the backscattering principle which is further described below.

[0070] Different from the conventional wireless communications device which actively generates its own signal, backscattering devices rely on reflecting an incident signal to transmit data. The encoded data is modulated by varying the amplitude (ASK), phase (PSK), or frequency (FSK) of the backscattered signal. More specifically, backscattering modulation is achieved by alternating between distinct load impedances of the antenna, with each impedance state leading to a unique characteristic of the reflected signal [4], Figure 4 illustrates a generic form of the backscattering circuitry including a matching network and an integrated circuit (IC).

[0071] There are two aspects of power that are relevant to the Ambient loT device:

[0072] • Absorbed power. This is the power that is energy harvested and can be used to drive the circuits within the tag.

[0073] • Reflected power. This is the power that is reflected as a backscattered signal.

[0074] Given the antenna and load impedances denoted as Za= Ra+ jXaand Zn= Rn+ jXn, n = 1,2, respectively, the reflection coefficient corresponding to each state is expressed as where * denotes the complex conjugate operation. Note that Figure 4 shows the antenna impedance Zaas Zanr. Note that it is possible for the load impedance to vary between more than two states, while in the present disclosure we consider binary state switching for the sake of simplicity. Ideally, when the load impedance is set to the complex conjugate of the antenna impedance at a certain state, n = 1 , Z-, = Z* , = 0 holds and thus the received power is completely absorbed by the communications device, leading to a lower reflection state. Different reflection coefficients can be obtained with different values of load impedance. For example, a value of Znthat is much greater than Zawill lead to a reflection coefficient close to 1 , leading to a higher reflection state. Note that in practice, the reflection coefficient |rn| depends on the manufacturing process and may vary within the range of (0,1).

[0075] The absorbed power can be calculated as where PavaHdenotes the power delivered from the antenna when the load impedance perfectly matches with the antenna impedance. In the literature the power transmission coefficient [5,6] is defined as:

[0076] . In fact, the power captured by the antenna will be split into two; one part is scattered back to the reader while another part is delivered to the tag. For the design of the reflection ratio, a trade-off needs to be considered to balance the need for both parts of the power.

[0077] Given Pavaii, the average power absorbed by the device can be calculated as Pin = Pavail

[0078] Where pn,n=i,2denote the ratio of time duration for each impedance state; p = p2holds if the probability of each impedance equals to the other (this also means that the same probability of Os and 1s appears in the encoded data if the backscattered signal uses a pure OOK waveform).

[0079] CW Emitter

[0080] The carrier-wave emitter (or CW emitter I C\NE) transmits a carrier wave signal (CWS) that can be used by the tag to backscatter a signal from. The tag may additionally harvest energy from the CWS or simply use the power from the CWS to power the circuitry in the tag (i.e. energy may not be stored by the tag but may be used for ongoing operations). The scenario is shown in Figure 5. Figure 5 shows a tag 1 with a backscattering module 70. The backscattered signal is backscattered on the CW signal by the backscattering circuit, which may have the structure shown in Figure 4. The tag 1 includes an energy harvesting module 72, which converts energy of the carrier wave signal into power to drive a microcontroller 74 and the backscattering module 70.

[0081] The tag can be powered by non-RF energy sources, such as via solar power. The tag can also I alternatively be powered by an RF energy source. The RF energy source may be the same signal as the CW emitter (the CW signal may both power the tag and provide a signal that can be backscattered from).

[0082] The CW emitter devices may take the following forms:

[0083] • Base station. The base station (e.g. gNodeB) acts as the CW emitter.

[0084] • Intermediate node. A reader may act as the CW emitter. The reader is a device that receives the backscattered signal, demodulates it and sends the result to the base station. The reader may also send signals (R2D - reader to device) to the tag.

[0085] • Dedicated node. The CW emitter may be a dedicated node whose purpose is to provide a CW signal that can be backscattered from. The CW signal can also be used to power the tag, as discussed above.

[0086] The tag may receive sufficient power to decode downlink signalling, but not have sufficient power to transmit a backscattered signal in the UL (there is insufficient link budget in the uplink). In an example, the tag can decode the AloT downlink based on ambient RF power, for example power that is received directly from the gNB. Note that the signals that are sent from a base station or reader to the tag are considered to be downlink signals from the perspective of the tag. These signals can be actually transmitted in uplink spectrum. A skilled artisan will understand when the term “downlink” refers to the topological direction of travel of a signal and when it refers to specific types of spectrum.

[0087] A CW emitter may be capable of transmitting different types of signal. For example, a CW emitter may be capable of transmitting a CW signal, as discussed above, which allows a tag to backscatter or harvest energy. Such a CW signal can be a single tone or multi-tone signal. In addition, a CW emitter may be able to transmit a reference signal. Such a reference signal may be a multi-tone signal, e.g. in the form of a reference signal used in LTE or NR networks. Examples include a sounding reference signal (SRS) or a demodulation reference signal (DMRS), however the CW emitter may be able to transmit other types of reference signals.

[0088] The protocol for Ambient loT operation can be based on a command I response type of protocol. The detection station (which might be the gNodeB) sends a downlink command signal with a command to the tag. For example, the downlink command signal could indicate to the tag that it should respond with its identity (such as an identity number). The downlink command signal could indicate some further aspect of how the tag should respond. For example, the downlink command signal may indicate an amount of frequency shift that should be applied to the response signal, or may indicate a time at which the response signal should be transmitted or higher layer message to respond with a sensor reading. Based on the downlink command signal, the tag responds with a backscattered signal, where the backscattered signal is backscattered on the carrier wave signal.

[0089] Figure 6 shows an example of an A-loT network. There are three CWEs illustrated in the figure; each CWE is scheduled by the gNB for the CW transmission to the A-loT device (named as ‘Tag’ in this figure). The tag may also receive a command from the gNB and respond accordingly, e.g., standby, data transmission and reflection in a manner known by the gNB.

[0090] In a general indoor scenario, A-loT devices (also called tags) are deployed and attached to objects for various purposes, e.g., inventory, environment monitoring, etc. Tags are connected to a cellular network which is served by a single gNB or reader. Since the tags can only conduct backscattering communications, a bi-static topology is shown in order to enhance the communication range; this is realized by the deployment of multiple carrier wave emitters (CWEs) which transmit CWSs to the tag and enable backscattering at the tag.

[0091] Capability of CWEs - CWEs can receive, process, and transmit OFDM-based multi-tone signals, for example control signals sent by a gNodeB or other controlling node. The CW that the CWEs transmit may be, for example, in the form of an unmodulated single-tone signal (however other types of tone may be used), which can be generated by only transmitting through a single OFDM subcarrier or other ways compatible to the OFDM based signal generation process.

[0092] Capability of tags - Depending on whether the tag can actively generate the signal or not, the tags are categorized into either active tags or (semi-) passive tags. Passive tags rely on backscattering communications. Active devices can actively generate a signal and transmit the signal at a desired frequency.

[0093] Passive tags cannot actively generate signals for transmission due to their low-complexity nature. They don’t support decoding OFDM-based multi-tone signals. They can decode signals that are sent on a R2D (reader to device, where the gNB can act as the reader) link when the R2D link uses a simple modulation scheme, such as OOK or FSK. This decoding could be done with a simple low power receiver, such as an envelope detector. For the D2R (device to reader) link, different backscattering modulation schemes may be applied, such as on-off keying (OOK), frequency shift keying (FSK), phase shift keying (PSK) and other schemes, given the incident CW signal.

[0094] Apart from the basic functionalities, e.g., data transmission, registration, and identification, etc., the tag is also able to be controlled, based on the command received from gNB on the R2D link, via its controller to achieve a certain reflection state, such as a high reflection state or a low / no reflection state. Note that the tag can exploit the difference between impedance states to yield various reflection ratios (as described above with reference to Fig. 4), e.g., constant absorption / reflection, etc. (i.e. high reflection and low / no reflection states can be achieved by changing the reflection ratios).

[0095] Depending on the availability of energy storage, tags are categorized into passive (without energy storage) and semi-passive (with energy storage) devices. An energy harvester is usually implemented to extend the life of the device and its type may include RF-based and other types of energy sources.

[0096] The tags have low accuracy clocks in order to reduce device complexity and to reduce tag power consumption. The tag is hence unable to accurately synchronise to the reader (e.g. gNB) and is unable to maintain accurate and consistent timing between synchronisation events (e.g. transmission of the Synchronization Signal Block (SSB)) as the tag’s clock would drift in the meantime.

[0097] Reader-to-Device (R2D) Signal

[0098] As discussed above, R2D signals may be transmitted from a reader to an A-loT device. The reader that transmits the R2D signal may be a base station or may be a UE, as discussed in [3] and shown in Figure 7, and as such both a base station and a UE that transmit an R2D signal may collectively be referred to as a reader or a transmitter. Although not shown in Figure 7, the same R2D signal may be received by more than one A-loT device.

[0099] It is expected that such R2D signals should be compatible with legacy OFDM-based systems in future deployments [8, 9], where these legacy OFDM-based systems are often referred to as cyclic prefix OFDM (CP-OFDM) systems. In particular, base stations or UEs according to existing 5G / NR wireless communications systems, such as those described above, are expected to transmit R2D signals in future 6G-I0T deployments. Accordingly, it is desirable that R2D signals can be generated using the same hardware as CP-OFDM systems. It is expected that the R2D packets may be transmitted (e.g. by a base station) simultaneously with NR packets, and as such the actual transmitted signal may be a superposition of the R2D packets and the NR packets. A- loT devices would then perform filtering in order to isolate the R2D signal from the superposed signal.

[0100] It is envisaged that R2D signals will be transmitted on a packet-by-packet basis. An example of such an R2D packet is shown in Figure 8 and includes a preamble followed by M OFDM symbols, however other structures are envisaged. Figure 8 shows a close up view of OFDM symbol M-1 , showing a cyclic prefix (CP) located at the start of the OFDM symbol, followed by a data portion which includes tail portion. The CP is a duplicate of the tail portion. This OFDM symbol structure shown in Figure 8 is the same as the OFDM symbol structure used in CP-OFDM systems. The CP in legacy NR / LTE systems allows for the use of low cost one tap channel equalization using fast Fourier transforms for decoding. The CP can also be used for subframe detection and timing correction. As mentioned above, R2D signals for A-loT applications should coexist with legacy NR downlink systems, and as such the waveform type of the R2D signal should conform to the CP rule (i.e. the CP is a copy of a tail portion of the OFDM symbol).

[0101] However, due to the low-complexity nature of the A-loT devices, the R2D signal carries information through amplitude variation in the time domain, e.g., OOK modulation. This differs from the conventional OFDM-based frequency-domain information carrying approach. Therefore, the R2D signal needs to be carefully designed such that the CP is properly included. However, the CP should be included in such a way that it does not interfere with the decoding of the R2D signal at the (low complexity) A-loT device.

[0102] In addition, as A-loT devices are of low complexity, it is challenging for these devices to maintain an accurate clock frequency. For example, the sampling frequency offset (SFO) can in some cases reach 104or 105ppm. While it is possible for devices to perform clock acquisition based on a preamble of the received signal (e.g. NR or R2D signal), the A-loT device may not be able to maintain an accurate clock based only on this initial clock information. In particular, since the time duration of the clock acquisition part may be short, the accuracy of the A-loT device’s derived clock may be poor. Support of continuous clock acquisition is one potential means of addressing this high SFO, however thus far the R2D signal does not support this functionality. It would therefore also be desirable to provide an R2D signal format that supports continuous clock acquisition such that the device can estimate and then correct the clock based on the reception of the R2D signal.

[0103] According to the invention, a reader device (i.e. a reader) transmits a reader-to-device (R2D) signal for receipt by a communications device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of the radio access interface, wherein the R2D signal is transmitted according to an ON-OFF-keying (OOK) structure, and wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device; a tail portion located at an end of the OFDM symbol; and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information for receipt by the communication’s device.

[0104] In particular, the R2D signals may be generated utilising an on-off-keying (OOK) scheme, commonly referred to as OOK-4, as shown in Figure 9. It should be appreciated that Figure 9 only represents one of the possibilities for signal generation and that the R2D signal may be generated using other OOK schemes. As illustrated in Figure 9, first the R2D signal may be determined in the time domain. That time-domain R2D signal is then converted into the frequency-domain via a fast Fourier transform (FFT). In some cases, the frequency-domain R2D signal may be rearranged through subcarrier shifting and truncation, as shown. The purpose of both operations is to preserve the OOK-like shape of the resulting time-domain R2D signal and ensure the retained subcarriers are within the corresponding subband assigned to the R2D link. An inverse FFT may be performed to recover a time-domain R2D signal. The tail portion is then copied (i.e. duplicated) to the CP portion.

[0105] According to the invention, the OOK structure / scheme utilised for generation of the R2D signal contains two portions: a data-carrying portion, and a tail portion. Unlike the conventional usage of OOK-4 scheme where only the data-carrying portion is generated, this invention provides an efficient approach of CP handling through the introduction of the tail portion, i.e., the CP of each OOK symbol block is the duplicate of the tail portion. In particular, after a tail portion is determined the tail portion is copied to the CP portion. It should be noted that the CP and tail portions may in some cases be coded differently and may use a different waveform structure. Furthermore, as per above, the OOK symbol block is incorporated in the OFDM symbol block and is superposed with NR signals.

[0106] In utilising this approach, an A-loT device may detect the CP portion of the R2D signal (i.e. the waveform). Furthermore, the R2D transmitter (i.e. the reader device, which may be a gNB or UE) may transmit an R2D signal with a CP. Accordingly, the R2D signal will be compatible with (and orthogonal to) other OFDM signals transmitted by the R2D transmitter. This approach also simplifies CP handling procedures compared to cases where the CP is inserted prior to performing an FFT. In addition, it is envisaged that the CP and tail portions may be utilised for one or more additional purpose, by indicating additional information for use by the A-loT device, as will be discussed later.

[0107] An example of the OOK signal structure of an OFDM symbol 1000 of the R2D signal is shown in Figure 10. Each OFDM symbol 1000 of the R2D signal includes a data portion 1020, a tail portion 1030, and a CP 1010 which is a duplicate of the tail portion 1030. The OOK structure is generated by appending the tail portion 1030 to the data portion 1020, and then duplicating the tail portion 1030 to the CP 1010. The duration of the CP 1010 is equal to the duration of the tail portion 1030. The OOK structure for the R2D signal comprises one or more ON signals, shown as a comparatively high amplitude, and one or more OFF signals, shown as a comparatively low amplitude.

[0108] It should be appreciated that the exact structure of the tail portion 1030 and CP 1010 may take a variety of forms, as will be discussed below. Furthermore, while in the example of Figure 10 and the other examples discussed herein the data portions include a Manchester-encoded signal, it should be appreciated that different data encoding schemes may be used for one, multiple, or all OFDM symbols of an R2D signal. In addition, it is noted that the data portion of the R2D signal may be compressed in time in order to allow the addition of the tail portion and CP. In particular, the data carried by the data portion is separate from the data (or other information) carried by the tail portion (and duplicated in the CP), such that the time duration of the data portion 1020 is shortened. However, as discussed herein, the addition of the tail portion 1030 and CP 1010 improve the overall robustness of the R2D signal, even when taking into account the reduced duration of the data portion 1020.

[0109] In some examples, the structure of the tail portion and CP may be predetermined (i.e. may correspond to known sequences), in this manner the A-loT device may search for the predetermined sequences in order to determine the locations of the CP and tail portion, for example using a correlation method, as discussed below. Use of predetermined sequences for the CP and tail portion is particularly useful for continuous clock acquisition, as the A-loT device can locate the CP and tail portion and use the location(s) to adjust its own clock. Such a predetermined sequence may be defined in specifications (i.e. predefined), indicated in the preamble of the R2D signal, or signaled to the A-loT in any other way (such as via a system information block (SIB)).

[0110] Figure 11 shows an example of an OFDM symbol 1100 of an R2D signal having a data portion 1120 as well as a tail portion 1130 and a CP 1110 which have a predetermined structure. In this example, the tail portion 1130 and CP 1110 have a high amplitude (i.e. high voltage level) corresponding to an ON signal. Use of an ON signal in the CP 1110 and tail portion 1130 is particularly advantageous for clock synchronization as the ON signal can be easily detected. In addition, the ON signal may in some cases be used by the A-loT device for ambient energy harvesting. Furthermore, for a Manchester-encoded signal, the ON signal for CP 1110 and tail portion 1130 guarantee an additional transition in the OFDM symbol compared to a purely Manchester-encoded signal (since either the first phase of the Manchester-encoded signal is OFF, leading to a transition at the start of the OFDM symbol, or the second phase of the Manchester-encoded signal is OFF, leading to a transition at the end of the OFDM symbol). These extra transitions further facilitate clock recovery / acquisition.

[0111] Figure 12 shows a further example of an OFDM symbol 1200 of an R2D signal having a data portion 1220 as well as a tail portion 1230 and a CP 1210 which have a predetermined structure. In this example, the tail portion 1230 and CP 1210 have a low amplitude (i.e. low voltage level) corresponding to an OFF signal. The OFF signals may be used for timing synchronization (i.e. clock acquisition / recovery) in the same manner as the ON signals of the example of Figure 11.

[0112] While the examples of Figures 11 and Figure 12 use a predetermined sequence for the CP and tail portion that is a signal of constant amplitude, it should be appreciated that the CP and tail portions may have one or more transitions in amplitude (i.e. transitions between an ON signal and an OFF signal). Figure 13 illustrates an example of such a CP and tail portion structure for an OFDM symbol 1300. The OFDM symbol 1300 of the R2D signal has a data portion 1320 as well as a tail portion 1330 and a CP 1310 which have a predetermined structure. In this example, the tail portion 1330 and CP 1310 include an ON signal which transitions to an OFF signal. Figure 14 shows a similar example of an OFDM symbol 1400 which is identical to that of Figure 13 (having the same data portion 1420), except that the tail portion 1430 and CP 1410 include an OFF signal which transitions to an ON signal. A single ON-OFF (or OFF-ON) transition within the tail portions (which will be duplicated in the CP) ensures that there will be an additional two transitions within the OFDM symbol (one in the CP portion and one in the tail portion), aiding clock recovery as the transitions are distinct to the signal (which may be referred to as the baseline signal) in the data portion. The transition may be located at a midpoint of the tail portion (and the CP) which may allow the A-loT device’s receiver to more easily identify the tail and CP portions of the signal by counting samples around those transitions, as discussed later. For example, if the tail portion is 5 samples long and a transition in the tail is identified at sample 3, samples 1 ,2, 3, 4, 5 can be identified as the tail and treated appropriately).

[0113] While Figures 13 and 14 use a predetermined sequence for the CP and tail portion that includes a single ON-OFF (or OFF-ON) transition, it should be appreciated that the CP and tail portions may have multiple transitions in amplitude (e.g. ON-OFF-ON, OFF-ON-OFF, ON-OFF-ON-OFF, OFF-ON-OFF-ON, etc.). Figure 10, already discussed, illustrates an example of an OFDM symbol 1000 having a data portion 1020 identical to those shown in Figures 11-14. The CP 1010 and tail portion 1020 include an OFF-ON-OFF signal. The presence of additional transitions facilitates identification of the CP and tail portions of the OFDM symbol, since these transitions are distinct to the signal (i.e. baseline signal) in the data portion 1020.

[0114] Figures 10-14 illustrate example signals (i.e. signal patterns / sequences) which may be utilised in the CP and tail portions of OFDM symbols for the R2D signal. As discussed above, these signal patterns may be predetermined and fixed, for example in order to allow an A-loT device to recover / acquire its clock timing, such that the only additional information provided by the CP and tail portion is for timing purposes. However, in other examples the signals in the CP and tail portions may not be predetermined, such that the CP and tail portion may themselves carry (i.e. indicate) data which is distinct from the data included in the data portion. In other words, the data portion of an OFDM symbol may indicate one or more bits of data according to the signal encoded in the data portion, and the CP and tail portion may collectively encode one or more other bits of data according to the signal encoded in the CP and tail portion.

[0115] As an example, the signal included in the CP and tail portion may indicate a particular bit of information. Figure 15 shows one implementation of this. In the example of Figure 15, the data portions 1520(1) and 1520(2) in a first and second OFDM symbol 1500(1), 1500(2) each indicate respective first data. The CP 1510(1) and tail portion 1530(1) of the first OFDM symbol 1500(1) has a particular signal (in this example an OFF-ON-OFF signal) which may be interpreted to correspond to a 0 bit value, while the CP 1510(2) and tail portion 1530(2) of the second OFDM symbol 1500(2) has a different signal (in this example an ON-OFF-ON signal) which may be interpreted to correspond to a 1 bit value). In this way, different signal patterns in the CP and tail portion of OFDM symbols may indicate different data. While this example refers only to two different signal patterns corresponding to 0 and 1 bit values, it should be appreciated that signals in the CP and tail portions may be mapped to data in a variety of different ways.

[0116] As the duration / length of the CP and tail portion is short compared to the data portion, the reliability with which the CP and tail portion can be detected is generally lower than the data portion. As such, the CP and tail portion may be repeated across multiple OFDM symbols. These may be consecutive or non-consecutive OFDM symbols. An example of this arrangement is shown in Figure 16, where the data portions 1620(1) and 1620(2) in a first and second OFDM symbol 1600(1), 1600(2) each indicate respective first data. The CP 1610(1) and tail portion 1630(1) of the first OFDM symbol 1600(1) has a particular signal (in this example an OFF-ON-OFF signal) which may be interpreted to correspond to a 0 bit value. The CP 1610(1) and tail portion 1630(1) may then be repeated in a subsequent (in this case consecutive) OFDM symbol 1600(2), such that CP 1610(2) and tail portion 1630(2) are identical to CP 1610(1) and tail portion 1630(1). By repeating the CP and tail portions, the combination of the CP and tail portion can be more reliably detected as the A-loT device’s receiver can perform repetition decoding on the repeated CP-tail portion pairs in order to increase the reliability of decoding of the data that is carried by the CP- tail portion pair. It should be appreciated that the CP-tail portion pair may in some cases be repeated across multiple subsequent OFDM symbols.

[0117] According to some examples, the data carried by the CP and tail portion may be dependent on the data carried by the data portion. In other words, the CP and tail portion may be a function of the data that is carried by the data portion. In such examples, the CP-tail portion pair and the data portion may be jointly decoded by the A-loT device. Figure 17 shows an example of an arrangement where the CP and tail portion are a function of the data that is carried by the data portion. In Figure 17, a data portion 1720(1) of a first OFDM symbol 1700(1) may indicate first data (in this example a 0 bit value), and a data portion 1720(2) of a second OFDM symbol 1700(2) may indicate second data (in this example a 1 bit value). As such, the CP 1710(1) and tail portion 1730(1) of the first OFDM symbol 1700(1) has a first signal pattern, while the CP 1710(2) and tail portion 1730(2) of the second OFDM symbol 1700(2) has a second signal pattern.

[0118] In the example shown in Figure 17, the data portions each carry a single bit of data and as such there is a 1 :1 correspondence between the data portions and the CP-tail portion pairs. Accordingly, if the A-loT device is unable to decode the data portion (or determines that the decoding of the data portion may be considered to be inaccurate (for example due to comparatively small differences in the detected amplitude of OFF and ON signals in the data portion)) but is able to decode the CP-tail pair, then the A-loT device may be able to determine the data carried by the data portion. However, in other examples, the data portions may carry more than one bit, such that there is an N:1 correspondence between the data portions and the CP-tail portion pairs. Accordingly, the CP-tail portion pair may not be a definitive indication of the data included in the data portion, however the CP-tail portion may still be used to provide an indication of the data within the data portion. For example, as mentioned above, the data portion and the CP-tail pair may be jointly decoded to determine the data included in the data portion. For example, log likelihood ratios may be taken from the baseline signal (in the data portion) and the CP-tail portion. Given that there can be less energy in the CP-tail portion (the CP and tail are typically shorter than the baseline R2D signal), the log likelihood ratios contribution from the CP- tail portion can be less than that from the baseline signal. Jointly decoding the CP-tail portion pair and the data portion may increase the robustness of the decoding process.

[0119] According to some examples, the CP and tail portions may be either an ON signal or an OFF signal but may be set according to an end or start of the data portion. An example of this arrangement is shown in Figure 18, which illustrates two OFDM symbols 1800(1), 1800(2). The first OFDM symbol 1800(1) has a data portion 1820(1) which starts with an ON signal and transitions to an OFF signal. In this example, the CP 1810(1) and tail portion 1830(1) are set such that the CP 1810(1) signal is an extension (earlier in time) of the initial (i.e. starting) signal of the data portion 1820(1), which in the case of the first OFDM symbol 1820(1) is an ON signal. As such, the tail portion 1830(1) is set to be the same as the starting / initial signal of the data portion 1820(1), and as such the tail portion 1830(1) is set to an ON signal. The tail portion 1830(1) is duplicated to the CP 1810(1) such that the CP 1810(1) is also set to an ON signal, thereby serving as an extension of the start of the data portion 1820(1). In Figure 18, a second OFDM symbol 1800(2), has a data portion 1820(2) which starts with an OFF signal and transitions to an ON signal. As the CP 1810(2) is set to be the same as the starting / initial signal of the data portion 1820(2) in the same manner as the first OFDM symbol 1800(1), the tail portion 1830(2) is set to an OFF signal. The tail portion 1830(2) is then duplicated to the CP 1810(2), which is also set to an OFF signal. Extending the data portion of an OFDM symbol with the CP improves the robustness with which the data portion can be detected.

[0120] Figure 19 illustrates the opposite example to Figure 18 whereby the tail portion is set to be an extension of the end (i.e. final) signal of the data portion. Figure 19 illustrates two OFDM symbols 1900(1), 1900(2). The first OFDM symbol 1900(1) has a data portion 1920(1) which starts with an ON signal and transitions to an OFF signal. In this example, the CP 1910(1) and tail portion 1930(1) are set such that the tail portion 1930(1) signal is an extension (later in time) of the end (i.e. final) signal of the data portion 1920(1), which in the case of the first OFDM symbol 1920(1) is an OFF signal. As such, the tail portion 1930(1) is set to be the same as the end signal of the data portion 1920(1), and as such the tail portion 1930(1) is set to an OFF signal, thereby serving as an extension of the end of the data portion 1920(1). The tail portion 1930(1) is duplicated to the CP 1910(1) such that the CP 1910(1) is also set to an OFF signal. In Figure 19, a second OFDM symbol 1900(2), has a data portion 1920(2) which starts with an OFF signal and transitions to an ON signal. As the tail portion 1930(2) is set to be the same as the ending signal of the data portion 1920(2) in the same manner as the first OFDM symbol 1900(1), the tail portion 1930(2) is set to an ON signal. The tail portion 1930(2) is then duplicated to the CP 1910(2), which is also set to an ON signal. Extending the data portion of an OFDM symbol with the CP improves the robustness with which the data portion can be detected.

[0121] It should be noted that generally for the examples according to the present disclosure, the total length of the data portion may be the total length of the OFDM symbol, minus the length of the CP, minus the length of the tail portion. However, in some cases this may not be the case. For example, with reference to Figure 18, as the CP 1810(1) is an early extension of the data portion 1820(1), the length of the first chip (i.e. the initial signal - in this case an ON signal) of the data portion 1820(1) of the first OFDM symbol 1800(1) may be considered to be effectively increased. However, this leads to the chips of the data portion 1820(1) having different effective lengths. Accordingly, in some cases, the length of the chips within the data portion may be adjusted such that in cases where the CP and tail portion are an early extension (as in Figure 18) or a (late) extension (as in Figure 19) of the data portion, the effective lengths of the chips of the data portion are equal. For example, in cases where the CP is an early extension of the data portion, the lengths of the chips of the data portion may be set such that the length of the first chip of the data portion plus the CP is equal to the length of each of the remaining chip(s) of the data portion. As an example, returning to Figure 18, the length of the first chip of the data portion 1820(1) may be shortened (by moving the timing location of the signal transition earlier), and the length of the second chip of the data portion 1820(1) increased, such that the total length of the CP 1810(1) plus the first chip of the data portion 1820(1) is equal to the length of the remaining chip(s) of the data portion 1820(1). The same principle may apply to OFDM symbol 1800(2), where the length of the first chip of the data portion 1820(1) may be set such that the length of the CP 1810(2) plus the first chip of the data portion 1820(2) is equal to the length of the remaining chip(s) of the data portion 1820(2). A similar approach to that discussed in relation to Figure 18 may be applied in cases where the tail portion is an extension of the end of the data portion, as in Figure 19. In such cases, the lengths of the chips of the data portion may be set such that the length of the final chip of the data portion plus the tail portion is equal to the length of each of the remaining chip(s) of the data portion. For example, the length of the second chip of the data portions 1920 may be reduced and the length of the first chip of the data portion 1920 increased such that the length of the second chip of the data portion 1920 and the tail portion 1930 is equal to the length of the first chip of the data portion 1920.

[0122] In an alternative arrangement, the effective lengths of the chips are based on both the length of the CP and the tail portion. For example, in Figure 18, it is apparent that the total length of signal associated with the first chip of the data portion 1820(1) (i.e. the total ON signal duration) is equal to the sum of the length of the first chip of the data portion 1820(1), the CP 1810(1) and the tail portion 1830(1). Hence in an example, in cases where the CP is an early extension of the data portion, the lengths of the chips of the data portion may be set such that the length of the first chip of the data portion plus the CP plus the tail portion is equal to the length of each of the remaining chip(s) of the data portion. As an example, returning to Figure 18, the length of the first chip of the data portion 1820(1) may be shortened (by moving the timing location of the signal transition earlier), and the length of the second chip of the data portion 1820(1) increased, such that the total length of the CP 1810(1) plus the first chip of the data portion 1820(1) plus the tail portion 1830(1) is equal to the length of the remaining chip(s) of the data portion 1820(1).

[0123] A similar approach to that discussed in relation to Figure 18 may be applied in cases where the tail portion is an extension of the end of the data portion, as in Figure 19. In such cases, the lengths of the chips of the data portion may be set such that the length of the final chip of the data portion plus the tail portion plus the CP is equal to the length of each of the remaining chip(s) of the data portion. For example, the length of the second chip of the data portions 1920 may be reduced and the length of the first chip of the data portion 1920 increased such that the length of the second chip of the data portion 1920 and the tail portion 1930 and the CP 1910 is equal to the length of the first chip of the data portion 1920.

[0124] While Figures 17-19 illustrate certain examples in which the data carried by the CP and tail portions may be dependent on the data carried by the data portion, it should be appreciated that the data carried by the CP and tail portion may be set based on the data carried by the data portion in a variety of other ways. For example, the data carried by the CP and tail portion may be set according to a parity check to be carried out by the receiving A-loT device. In other words, the CP and tail portion may carry a bit (i.e. a 0 or a 1 value), which may be referred to as a parity bit, which has a value set according to the data in the data portion and a parity system (to be used by the A-loT device in a parity check). For example, the parity bit may be set according to a bitlevel parity check, whereby the parity bit is set such that the sum of the encoded bits (e.g. in the data portion(s) of a single OFDM symbol of the R2D signal) is either odd (if an odd parity system is used) or even (if an even parity system used). The parity bit may be indicated by a particular waveform (i.e. signal) in the CP and tail portions.

[0125] In some cases, instead of a bit-level parity check a chip-level parity check may be used. In such cases, the value of the parity bit in the CP and tail portion is set based on the chips within the data portion of an OFDM symbol. In particular, each OFDM symbol of the R2D signal is formed of a plurality of chips of a particular length, where each chip is set to either an OFF value or an ON value, such that any OFF-ON transition occurs between chips. A chip level parity check may then work such that the sum of each of the chips of the OFDM symbol (assuming e.g. OFF- 0’ and ON- 1’) is either odd or even, based on whether an odd or even parity system is used. The parity bit is therefore set such that the chip-level parity check returns an appropriate odd or even value. In the examples illustrated herein, the data portion carries a Manchester encoded signal (a pulse position modulation encoded signal) whereby the signal / waveform has a structure where only one chip is active in a defined time window (for example, for Manchester encoding one chip out of every two is active, and for 4PPM (pulse position modulation) encoding one chip out of every four is active). In such cases, the chip-level parity is always odd (only one chip is ever active). The concept of parity can be further extended in such encoding schemes by basing the parity check on the position of the active chip. For example, for 4PPM encoding odd parity may be declared if either the first or third chips are active and even parity may be declared if either the second or fourth chips are active.

[0126] By utilising the CP and tail portion to carry a parity bit for a parity check, the need for cyclic redundancy check (CRC) bits may be removed, thereby enhancing system efficiency (as the signal can be transmitted in a shorter time). Alternatively, the parity bits could be used to aid in error location and correction. For example, if a parity error were indicated in one location and the CRC failed, the packet could be decoded with the next most likely bit decision in the region of the parity error, and the CRC could be checked again. This would therefore provide a degree of error correction capability.

[0127] As discussed above, the CP and tail portion may either have a predetermined signal (e.g. for clock acquisition / recovery purposes) or may have a signal that carries additional data. In both cases, the tail portion of an OFDM symbol may form a continuous / contiguous pattern with the CP of a subsequent (i.e. consecutive / next) OFDM symbol. In other words, the tail portion of a first OFDM symbol may form a continuous signal pattern with a CP of an immediately following OFDM symbol. An example of this arrangement is shown in Figure 20, which includes a first OFDM symbol 2000(1) and a second OFDM symbol 2000(2) immediately following the first OFDM symbol 2000(1). The first OFDM symbol comprises a CP 2010(1), a data portion 2020(1), and a tail portion 2030(1), where the CP 2010(1) and tail portion 2030(1) have the same waveform (i.e. signal), in this case an OFF-ON signal. The second OFDM symbol 2000(2) also includes a CP 2010(2), a data portion 2020(2), and a tail portion 2030(2). In this example, the tail portion 2030(1) is contiguous with the CP 2010(2), and therefore as the tail portion 2030(1) ends with an ON signal, the CP 2010(2) begins with an ON signal. This effectively increases the duration of the ON signal (or any other signal that is contiguous across a tail portion and subsequent CP) such that it can be more reliably detected at an A-loT device. Tail portions and subsequent CPs may be contiguous for substantially any number of OFDM symbols. If the tail portions and subsequent CPs are contiguous for all OFDM symbols of the R2D signal, then the maximum amount of data which may be inferred from the CP and tail portions may be limited, however such an arrangement is useful for clock acquisition / recovery purposes for the A-loT device. Alternatively, the tail portions and subsequent CPs may only be contiguous for a set number of OFDM symbols, such that the rule may be broken in order to provide additional data to the A-loT device.

[0128] As shown in the foregoing examples, the CP and tail portions may have a shorter duration than the data portion. As such, the reliability / robustness of the detection of the CP and tail portion by the A-loT device may be comparatively low. Therefore, in order to increase the reliability with which the A-loT device may detect the CP and tail portion, the reader device may transmit the CP and tail portion with an increased amplitude. In other words, ON signals of the CP and tail portion may be transmitted with an amplitude that is greater than an amplitude of ON signals of the data portion. Such an example is shown in Figure 21 , which illustrates an OFDM symbol 2100 having a CP 2110, data portion 2120, and tail portion 2130. The data portion 2120 includes one or more ON signals having a first amplitude, and the CP 2110 and tail portion 2130 each include one or more ON signals having a greater / higher amplitude than the ON signals of the data portion 2120. By increasing the amplitude of the CP 2110 and tail portion 2130, the amount of energy contained within the CP 2110 and tail portion 2130 is increased, thereby improving reliability of detection. This increased amplitude may also be useful for energy harvesting for A-loT devices with energy harvesting capabilities.

[0129] Increasing the amplitude of the CP-tail results in higher peak-to-average power ratio (PAPR) of the R2D signal. In some scenarios, the signal transmitted by the reader device incorporates only the R2D signal, while in other scenarios, the signal transmitted by the reader device incorporates both the R2D signal and legacy NR signal. Careful R2D signal design, as discussed above, means that neither of these scenarios will impose a burden on the power amplifier more significantly than for a conventional NR OFDM system. This is because the amplitude can be adjusted by the reader device for acceptable PAPR in the first scenario (no legacy NR signals) in order to not exceed a PAPR limit. For example, an amplitude ratio (of CP-tail to baseline R2D signal) of approximately 1.5 (a power ratio of approximately 2.25) is optimal for decoding performance, and this power ratio is not significant compared to that for a legacy NR OFDM signal. For the latter scenario (legacy NR signals also transmitted), the PAPR is calculated based on the superposition of both the R2D and NR signals. Since NR signals are likely to occupy more subcarriers than the R2D signal, the NR signal may contribute more to the PAPR than the CP-tail contribution from the A-loT signal in this example.

[0130] In some cases, the A-loT device may be aware of the relative amplitude of the CP and tail portion, which may aid the A-loT device in decoding the R2D signal. For example, the A-loT device may apply a reliability weighting to the CP and tail portion relative to the baseline signal of the data portion during decoding, where the reliability weighting of the CP and tail portion may depend on the relative amplitude of the CP and tail portion as compared to the baseline signal. It is noted that the reliability weighting of the CP and tail portion may also depend on other factors such as a duration of the CP and tail portion, or a number of repetitions of the CP and tail portion. The A- loT device may therefore apply a higher weighting to the CP and tail portion for the decoding process if the CP and tail portion are known to have a higher relative amplitude. As such, the A- loT device may be aware of the relative amplitude of the CP and tail portion. The relative amplitude of the CP and tail portion may be defined in specifications (i.e. predefined) or may be signaled to the A-loT device. The relative amplitude of the CP and tail portion may be signaled to the A-loT device in a number of different ways, such as broadcast for receipt by the A-loT device (and one or more other devices) e.g. in a system information block (SIB). Alternatively, the relative amplitude of the CP and tail portion may be signaled to the A-loT device separately from the R2D signal. Alternatively, the relative amplitude of the CP and tail portion may be indicated in the preamble of the R2D signal, for example such that a first preamble indicates a first relative amplitude, and a second preamble indicates a second relative amplitude.

[0131] As has been discussed above, the CP and tail portion may be utilised for a variety of different purposes, such as clock acquisition, data transmission, and error correction / mitigation. However, for each of these processes the A-loT device detects / decodes the CP and tail portion to determine the information (e.g. clock signal, data, or parity bit) indicated by the CP and tail portion. This may be done using a correlation method (i.e. a correlation calculation). Such a correlation method may be based on a baseband signal in the digital domain. The baseband signal may be obtained by passing the received RF signal through a band-pass filter, a rectifier, a low-pass filter, followed by an analog-to-digital (ADC) quantizer e.g. a 4-bit ADC. As the signal is modulated by an OOK scheme, the baseband signal is real-valued and the correlation may be calculated in the real domain. It should be appreciated that this is just one approach for determining the baseband signal, and that the baseband signal may be determined in other ways.

[0132] The correlation method used to identify the CP and tail portion may be any one of a number of different correlation methods. For example, the correlation method may be an autocorrelation method. Such an autocorrelation method may detect the CP and tail portion without knowing the signal pattern in the CP and tail portion in advance. Such an approach is therefore useful in cases where the signal in the CP and tail portion is not predetermined. The autocorrelation method may be performed in a number of ways, such as based on the CP and / or tail portion being a predetermined number of samples (i.e. discrete time periods to which the A-loT device assigns a particular value for the received signal, such as 0 or 1). For example, if the CP is known to be 20 samples in length and the A-loT device has identified the CP location, the tag can correlate those 20 samples with the incoming received signal to find an autocorrelation spike / peak (i.e. a highest autocorrelation value) when the CP and tail portion align in the autocorrelation process, thereby identifying the location of the tail portion in the received signal. The A-loT device may then in some cases reset / realign its timing (i.e. clock) assumption based on this autocorrelation spike in order to determine the location of the CP of the following OFDM symbol. One example of the autocorrelation method is that the A-loT device may utilise the CP (which is sampled according to the A-loT device’s clock) as the correlation sequence in order to calculate a sequence-wise correlation with the rest of the sampled sequence. The highest value of autocorrelation will occur when the CP and tail portion are aligned in the autocorrelation process, and as such the A-loT is able to identify the location of the tail portion. Based on the detected CP-tail portion pair, the A- loT device may be able to extract the baseline signal in the data portion of the OFDM symbol as the data-carrying signal. In other words, in using an autocorrelation method to detect the CP and tail portion, the A-loT device may detect the CP and tail portion by performing a correlation measurement for the portion of the received signal within which the highest autocorrelation value exists. That is, a region of the signal in which the tail portion is located will have a high autocorrelation value. Accordingly, the A-loT device may count a number of samples in said region and thus determine the location of the tail portion.

[0133] As discussed above, in some cases the A-loT device may consider both the tail portion of a particular OFDM symbol and the CP of the next OFDM symbol for the purposes of decoding. For example, with reference to Figure 20 for the purposes of illustration, jointly considering the tail portion 2030(1) in the first OFDM symbol 2000(1) and the CP 2010(2) in the second OFDM symbol 2000(2) may help to mitigate the confusion of counting samples in the clock acquisition procedure if the SFO is large, e.g., approximately 105ppm or greater. In particular, assuming that a CP accounts for 7% of an OFDM symbol duration and a data portion of the OFDM symbol includes 128 samples, the entire OFDM symbol may include 137 samples (128 x (1+7%). If the SFO is 105ppm (i.e. 10%), the resulting number of samples may be approximately 150 (i.e. incorrect by 13 samples (approximately 10%). Utilising both the tail portion 2030(1) and CP 2010(2) for performing the autocorrelation may help to mitigate this error.

[0134] In other examples, the correlation method may be based on a predetermined sequence. In particular, if the signal pattern in the CP and tail portion is known (e.g. if the CP and tail portion is to be used for clock acquisition / recovery), the received signal may be correlated with the predetermined sequence to identify regions of high correlation corresponding to the CP and tail portion.

[0135] In some cases, the CP and tail portion may be detected by the A-loT device on a block-by-block basis, or on a packet-by-packet basis. In other words, the A-loT device may detect the CP and tail portions for a subset of the OFDM symbols of the R2D packet (i.e. a block of OFDM symbols) at a time, rather than for the entire packet (i.e. for all OFDM symbols of the R2D signal) at a time. The block-by-block detection process could, for example, operate in a step-wise fashion or in a sliding window fashion. In a step-wise fashion, blocks A and B are distinct and processed separately, whereas in a sliding window fashion, the blocks are considered to be the most recent set of received OFDM symbols and the current block may contain some OFDM symbols from the previous block. One advantage of the block-by-block method is that the A-loT device may continually recover its clock during the detection, i.e., the A-loT device can correct its clock frequency based on the detected CP-tail at each OFDM symbol block, and the A-loT device does not need to store an entire packet’s worth of samples to perform the detection. It should be noted that in some cases the A-loT device may fail to detect the CP and tail portion, for example due to poor signal-to-noise (SNR) conditions for a number of OFDM symbol blocks. If this occurs, the A- loT device may perform the CP and tail portion identification based on the A-loT device’s knowledge of CP and tail portion locations from previous blocks.

[0136] In addition to detecting the location of the CP and tail portion, and in some cases identifying the information indicated by the CP and tail portion, the A-loT device may use the detection of the CP and tail portion to estimate the SFO of the A-loT device. That is, given that the A-loT device successfully detects the CP-tail of a single OFDM symbol, it can estimate the time drift caused by the SFO by comparing the counted number of samples of the data portion with a reference number of samples. In other words, the A-loT device may be aware that the data portion (i.e. duration between the CP and tail portion) should be a predetermined number of samples in length, and may compare the number of samples actually observed between the detected CP and tail portion with this predetermined number of samples to determine the offset in terms of number of samples, and therefore the SFO. Based on the calculation of its SFO, the A-loT device may adjust its sampling frequency to reduce the SFO.

[0137] The actual data portion length (in number of samples) can be derived based on the counted index of the largest correlation value and the length of the CP. Meanwhile, the reference number of samples could be determined in a number of different ways, such as based on each OOK data chip length and the total number of OOK data chips incorporated in a single OFDM symbol, where the A-loT device may be aware of the OOK data chip length and the total number of OOK data chips incorporated in a single OFDM symbol in advance. For example, the OOK data chip length and the total number of OOK data chips incorporated in a single OFDM symbol may be predefined in specifications or transmitted to the A-loT device (e.g. from the reader device) in signaling, such as in the preamble of the R2D signal, or other signaling such as a system information block. Alternatively, the number of samples of the data portion may be predefined or signaled to the A- loT device in a corresponding manner. It should be appreciated that various information may be signaled to the A-loT device regarding the R2D signal, such as the chip duration of the data- carrying portion of the R2D signal (i.e. the baseline R2D signal), the CP duration, and the number of chips in the data-carrying portion, which may be used in estimating the SFO. For example, the reference number of samples of the data-carrying portion may be 238 samples, and based on the CP-tail detection process, the A-loT may count the actual number of samples of the data-carrying sequence as 240. This means that the clock frequency possessed by the A-loT device is (240- 238) / 238 = 0.84% higher than the reference frequency. The A-loT device may then reduce its clock frequency by 0.84% based on the estimate. Note that the tag can oversample the signal to obtain a more accurate SFO estimation and thus improved clock correction. Furthermore, by performing the correlation using a repeated CP-tail portion pair (as in Figure 16) the sampled CP of an earlier OFDM symbol (the earlier in the OFDM symbol the sample is taken the least affected the CP will be by SFO) may be used for calculation of the SFO over multiple OFDM symbols (in which the CP-tail portion pair is repeated), thereby providing a more accurate calculation of the SFO.

[0138] In some examples, the A-loT device may correlate the samples of the received sequence with reference sequences by a blind detection process, based on different hypotheses of the SFO. In other words, the A-loT device may perform a correlation utilising multiple reference sequences of different lengths. The reference sequence with the highest correlation with the actual signal may then be utilised to estimate an error in the clock of the A-loT device (i.e. to estimate the SFO). The reference sequences can be based on known transmitted sequences. For example, for the case of a transmitted OFDM symbol of duration 128 samples (containing a CP and tail portion), the A-loT device can create reference sequences of duration 127, 128 and 129 samples long. The 127 sample sequence is created by deleting one sample from a known transmitted sequence. The 129 sample sequence is created by inserting one sample from a known transmitted sequence. Depending on which reference sequence gives the best correlation, the A-loT device can estimate the SFO compared to the reader’s clock. For example, if the 127 sample sequence provides the best correlation, the A-loT device may determine that its clock is slow by one sample out of every 128 samples compared to the reader device’s clock. Conversely, if the 129 sample sequence provides the best correlation, the A-loT device may determine that its clock is fast by one sample out of every 128 samples compared to the reader device’s clock. Further conversely, if the 128 sample sequence provides the best correlation, the A-loT device may determine that its clock is the same as the reader device. The estimate of the discrepancy between the A-loT device’s clock and the reader’s clock may in some cases be used to derive a calibrated clock for the A-loT device.

[0139] Figure 22 illustrates a flowchart for a method 100 for a reader device according to an example of the present disclosure. Step S110 includes transmitting a reader-to-device (R2D) signal for receipt by a communications device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of the radio access interface, wherein the R2D signal is transmitted according to an ON-OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device; a tail portion located at an end of the OFDM symbol; and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information for receipt by the communication’s device.

[0140] Figure 23 illustrates a flowchart for a method 200 for a communications device according to an example of the present disclosure. Step S210 includes receiving a reader-to-device (R2D) signal from a reader device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of a radio access interface of the wireless communications network, wherein the R2D signal corresponds to an ON-OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device, a tail portion located at an end of the OFDM symbol, and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information. Step S220 includes detecting the CP and tail portion to identify the additional information. Step S230 includes identifying the first data. Those skilled in the art would further appreciate that methods, 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, provided that these are within the scope of the claims.

[0141] The methods described herein may also be embodied or encoded in a computer-readable medium, such as a computer-readable storage medium, containing instructions. Instructions embedded or encoded in a computer-readable medium may cause a programmable processor, or other processor, to perform the method, e.g., when the instructions are executed. Computer- readable media may include non-transitory computer-readable storage media and transient communication media. Computer readable storage media, which is tangible and non-transitory, may include random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), flash memory, a hard disk, a CD-ROM, a floppy disk, a cassette, magnetic media, optical media, or other computer-readable storage media. The term “computer-readable storage media” refers to physical storage media, and not signals, carrier waves, or other transient media. As noted above, computer readable media may include transient communication media. Such communication media may occur within a single computer system or between multiple computer systems, and may take the form of transient signal-conveying media such as carrier waves and transmission signals.

[0142] Therefore, from one perspective there has been described methods, reader devices, communications devices, and circuitry are provided for providing a R2D signal that is compatible with legacy OFDM-based systems, where the R2D signal includes a data portion of reduced length, a cyclic prefix (CP), and a tail portions, where the CP is a duplicate of the tail portion. The CP and tail portion may be predetermined signals, or may be used to carry information, for example information based on data within the data portion, or standalone data.

[0143] Particular examples of the present disclosure are set out in the following numbered clauses:

[0144] 1. A method of operating a reader device forming part of a wireless communications network and configured to transmit signals to and / or to receive signals from one or more other devices of the wireless communications network via a radio access interface between the reader device and the one or more other devices, the method comprising: transmitting a reader-to-device (R2D) signal for receipt by a communications device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of the radio access interface, wherein the R2D signal is transmitted according to an ON- OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device; a tail portion located at an end of the OFDM symbol; and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information for receipt by the communication’s device. 2. The method according to any preceding clause, wherein the second signal is a predetermined synchronisation signal, and wherein the additional information is a clock timing.

[0145] 3. The method according to clause 1 or clause 2, wherein the second signal is an ON signal.

[0146] 4. The method according to clause 1 or clause 2, wherein the second signal is an OFF signal.

[0147] 5. The method according to clause 1 or clause 2, wherein the second signal is a signal with one or more amplitude transitions between an ON signal and an OFF signal.

[0148] 6. The method according to clause 5, wherein the second signal is an ON signal which transitions to an OFF signal.

[0149] 7. The method according of clause 5, wherein the second signal is an OFF signal which transitions to an ON signal.

[0150] 8. The method according to clause 5, wherein the second signal is a signal with a plurality of amplitude transitions between an ON signal and an OFF signal.

[0151] 9. The method according to any preceding clause, wherein the additional information is second data for receipt by the communications device, and wherein the second signal is based on the second data.

[0152] 10. The method according to clause 9, wherein the second data is a 0 bit value or a 1 bit value, and wherein the second signal indicates either the 0 bit value or the 1 bit value.

[0153] 11. The method according to clause 9 or clause 10, wherein the second data indicated by the second signal is based on the first data included in the data portion.

[0154] 12. The method according to clause 11 , wherein the second data indicated by the second signal is a parity bit having a value set according to the first data and a parity system.

[0155] 13. The method according to clause 12, wherein the parity system is a bit-level parity system, and wherein the parity bit has a value set according to one or more bits included in the first data.

[0156] 14. The method according to clause 12, wherein the parity system is a chip-level parity system, and wherein the parity bit has a value set according to one or more ON signals and / or one or more OFF signals included in the first signal.

[0157] 15. The method according to any of clauses 9-14, wherein the second data is indicative of the first data indicated by the first signal.

[0158] 16. The method according to any of clauses 9-15, wherein the second signal is repeated in one or more subsequent OFDM symbols.

[0159] 17. The method according to any preceding clause, wherein the second signal is an OFF signal or an ON signal, and wherein the second signal is an extension of a final chip of a plurality of chips making up the data portion.

[0160] 18. The method according to clause 17, wherein a length of the plurality of chips is set such that a length of the final chip plus the tail portion is equal to a length of each of the remaining chips of the plurality of chips of the data portion.

[0161] 19. The method according to clause 17, wherein a length of the plurality of chips is set such that a length of the final chip plus the CP and tail portion is equal to a length of each of the remaining chips of the plurality of chips of the data portion. 20. The method according to any preceding clause, wherein the second signal is an OFF signal or an ON signal, and wherein the second signal is an early extension of an initial chip of a plurality of chips making up the data portion.

[0162] 21. The method according to clause 20, wherein a length of the plurality of chips is set such that a length of the initial chip plus the CP is equal to a length of each of the remaining chips of the plurality of chips of the data portion.

[0163] 22. The method according to clause 20, wherein a length of the plurality of chips is set such that a length of the initial chip plus the CP and tail portion is equal to a length of each of the remaining chips of the plurality of chips of the data portion.

[0164] 23. The method according to any preceding clause, wherein an end of the second signal of the tail portion is contiguous with a start of a CP of a next OFDM symbol.

[0165] 24. The method according to any preceding clause, wherein an amplitude of an ON signal of the second signal has a higher amplitude than an amplitude of an ON signal of the first signal.

[0166] 25. The method according to clause 24, wherein the amplitude of the ON signal of the second signal is indicated in specifications.

[0167] 26. The method according to clause 24, wherein the amplitude of the ON signal of the second signal is indicated in a preamble of the R2D signal.

[0168] 27. The method according to clause 24, further comprising: transmitting, to the communications device and separate prior to the R2D signal, an indication of the amplitude of the ON signal of the second signal.

[0169] 28. The method according to clause 27, wherein the indication of the amplitude of the ON signal of the second signal is included in a system information block (SIB).

[0170] 29. The method according to any preceding clause, wherein the first signal is Manchester- encoded.

[0171] 30. The method according to any preceding clause, wherein the first data comprises one or more bits.

[0172] 31. The method according to any preceding clause, wherein the reader device is an infrastructure equipment of the wireless communications network, and wherein the one or more other devices comprise one or more communications devices.

[0173] 32. The method according to any of clauses 1-30, wherein the reader device is a communications device, and wherein the one or more other devices comprise an infrastructure equipment of the wireless communications network.

[0174] 33. The method according to any preceding clause, wherein the communications device is of a first type, wherein the first type of communications device is one of a plurality of types of communications device configured to communicate with the wireless communications network, and the first type of communications device has a reduced hardware complexity compared with at least one other type of communications device of the plurality of types of communications device.

[0175] 34. The method according to clause 33, wherein the at least one other type of communications device is a mobile phone. 35. The method according to any preceding clause, wherein the communications device is an internet-of-things (loT) device.

[0176] 36. The method according to clause 35, wherein the loT device is an ambient loT device.

[0177] 37. The method according to any preceding clause, wherein the communications device is a Machine-Type-Communication (MTC) device.

[0178] 38. The method according to any preceding clause, wherein the communications device has no Radio Resource Control (RRC) state with the wireless communications network.

[0179] 39. The method according to any preceding clause, wherein transmitting the R2D signal comprises generating the R2D signal for transmission using the OOK structure.

[0180] 40. The method according to clause 39, wherein generating the R2D signal for transmission using the OOK structure comprises: determining the OOK structure comprising the data portion and the tail portion; performing a fast Fourier transform on the OOK structure to obtain a frequency-domain signal; performing one or more modifications to the frequency-domain signal; performing an inverse fast Fourier transform on the modified frequency-domain signal to obtain a time-domain signal comprising the data portion and the tail portion; adding the CP to the time-domain signal by duplicating the tail portion to precede the data portion, to obtain the R2D signal for transmission.

[0181] 41. A reader device configured to form part of a wireless communications network, the reader device comprising: transceiver circuitry configured to transmit signals to and / or to receive signals from one or more other devices of the wireless communications network via a radio access interface between the reader device and the one or more other devices, and controller circuitry, the transceiver and controller circuitry configured to, in combination: transmitting a reader-to-device (R2D) signal for receipt by a communications device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of the radio access interface, wherein the R2D signal is transmitted according to an ON- OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device; a tail portion located at an end of the OFDM symbol; and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information for receipt by the communication’s device. 42. Circuitry for a reader device configured to form part of a wireless communications network, the reader device comprising: transceiver circuitry configured to transmit signals to and / or to receive signals from one or more other devices of the wireless communications network via a radio access interface between the reader device and the one or more other devices, and controller circuitry, the transceiver and controller circuitry configured to, in combination: transmitting a reader-to-device (R2D) signal for receipt by a communications device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of the radio access interface, wherein the R2D signal is transmitted according to an ON- OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device; a tail portion located at an end of the OFDM symbol; and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information for receipt by the communication’s device.

[0182] 43. A method of operating a communications device configured to transmit signals to and / or to receive signals from a reader device of a wireless communications network, the method comprising: receiving a reader-to-device (R2D) signal from a reader device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of a radio access interface of the wireless communications network, wherein the R2D signal corresponds to an ON- OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device, a tail portion located at an end of the OFDM symbol, and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information; detecting the CP and tail portion to identify the additional information; and identifying the first data.

[0183] 44. The method according to clause 43, wherein the communications device detects the CP and tail portion using a correlation method.

[0184] 45. The method according to clause 44, wherein the correlation method comprises an autocorrelation method which samples the R2D signal to identify the CP and tail portion. 46. The method according to clause 45, wherein the autocorrelation method comprises comparing correlation values for a plurality of sample counts for one or more OFDM symbols of the R2D signal.

[0185] 47. The method according to clause 45 or clause 46, wherein the autocorrelation method comprises identifying a location of the tail portion based on an identified correlation between the R2D signal and the second signal of the CP.

[0186] 48. The method according to any of clauses 39-47, wherein correlation method comprises correlating the R2D signal according to a clock of the communications device to identify the CP and tail portion.

[0187] 49. The method according to clause 44, wherein the correlation method comprises correlating the R2D signal with a predetermined signal pattern for the CP and tail portion.

[0188] 50. The method according to any of clauses 44-49, wherein the correlation method is performed separately for a plurality of blocks of OFDM symbols of the R2D signal, wherein the blocks of OFDM symbols are each a subset of the OFDM symbols of the R2D signal.

[0189] 51. The method according to any of clauses 44-49, wherein the correlation method is performed collectively for the entirety of the R2D signal.

[0190] 52. The method according to any of clauses 43-51 , further comprising: adjusting a clock timing for the communications device according to the detected CP and tail portion.

[0191] 53. The method according to any of clauses 43-52, further comprising: estimating a sampling frequency offset of the communications device based on a timing of the detected CP and tail portion.

[0192] 54. The method according to clause 53, wherein estimating the sampling frequency offset is based on comparing a detected number of samples forming the data portion with a predetermined number of samples for the data portion.

[0193] 55. The method according to clause 54, wherein the predetermined number of samples is determined based on a chip length for the OOK structure and a total number of chips in the OFDM symbol.

[0194] 56. The method according to clause 55, wherein the chip length and the total number of chips is either: defined in specifications, or received by the communications device in signalling from the wireless communications network.

[0195] 57. The method according to any of clauses 53-54, further comprising: adjusting the sampling frequency of the communications device according to the estimated sampling frequency offset.

[0196] 58. The method according to any of clauses 43-57, wherein each OFDM symbol of the R2D is formed of a plurality of chips, wherein the preamble of the R2D signal indicates a total number of chips of the R2D signal, and / or a duration of each of the plurality of chips. 59. The method according to clause 58, wherein the total number of chips and / or the chip duration is indicated by a preamble of the R2D signal.

[0197] 60. The method according to clause 58 or clause 59, wherein an indication of the total number of chips and / or the chip duration is received from the reader device in signalling separate from the R2D signal.

[0198] 61. The method according to clause 58, wherein the total number of chips and / or the chip duration is defined in specifications.

[0199] 62. The method according to any of clauses 43-61 , wherein the additional information is second data, and wherein the second signal is based on the second data.

[0200] 63. The method according to clause 62, wherein the second data is indicative of the first data, and wherein the identifying the first data is based on the identified second data.

[0201] 64. The method according to clause 63, wherein identifying the first data is based on assigning a first weighting to the received first signal and a second weighting to the received second signal according to the respective robustness of the first signal and the second signal.

[0202] 65. The method according to clause 64, wherein the second weighting is set to a higher value based on an amplitude of an ON signal of the second signal being higher amplitude than an amplitude of an ON signal of the first signal.

[0203] 66. The method according to clause 64 or clause 65, wherein the second weighting is set to a higher value based on an end of the second signal of the tail portion being contiguous with a start of a CP of a next OFDM symbol.

[0204] 67. The method according to clause 62 or clause 63, wherein the second data indicated by the second signal is a parity bit having a value set according to the first data and a parity system, and wherein identifying the first data is based on performing a parity check according to the parity system using the parity bit.

[0205] 68. The method according to clause 67, wherein the parity system is a bit-level parity system, and wherein the parity bit has a value set according to one or more bits included in the first data.

[0206] 69. The method according to clause 67, wherein the parity system is a chip-level parity system, and wherein the parity bit has a value set according to one or more ON signals and / or one or more OFF signals included in the first signal.

[0207] 70. The method according to any of clauses 43-69, wherein the second signal is a predetermined signal pattern.

[0208] 71. The method according to any of clauses 43-70, wherein the second signal is an ON signal.

[0209] 72. The method according to any of clauses 43-70, wherein the second signal is an OFF signal.

[0210] 73. The method according to any of clauses 43-70, wherein the second signal is a signal with one or more amplitude transitions between an ON signal and an OFF signal.

[0211] 74. The method according to clause 73, wherein the second signal is an ON signal which transitions to an OFF signal.

[0212] 75. The method according of clause 73, wherein the second signal is an OFF signal which transitions to an ON signal. 76. The method according to clause 73, wherein the second signal is a signal with a plurality of amplitude transitions between an ON signal and an OFF signal.

[0213] 77. The method according to any of clauses 43-76, wherein the second signal is an OFF signal or an ON signal, and wherein the second signal is an extension of a final chip of a plurality of chips making up the data portion.

[0214] 78. The method according to clause 77, wherein a length of the plurality of chips is set such that a length of the final chip plus the tail portion is equal to a length of each of the remaining chips of the plurality of chips of the data portion.

[0215] 79. The method according to clause 77, wherein a length of the plurality of chips is set such that a length of the final chip plus the CP and tail portion equal to a length of each of the remaining chips of the plurality of chips of the data portion.

[0216] 80. The method according to any of clauses 43-76, wherein the second signal is an OFF signal or an ON signal, and wherein the second signal is an early extension of an initial chip of a plurality of chips making up the data portion.

[0217] 81. The method according to clause 80, wherein a length of the plurality of chips is set such that a length of the initial chip plus the CP is equal to a length of each of the remaining chips of the plurality of chips of the data portion.

[0218] 82. The method according to clause 80, wherein a length of the plurality of chips is set such that a length of the initial chip plus the CP and tail portion is equal to a length of each of the remaining chips of the plurality of chips of the data portion.

[0219] 83. The method according to any of clauses 43-80, wherein an end of the second signal of the tail portion is contiguous with a start of a CP of a next OFDM symbol.

[0220] 84. The method according to any of clauses 43-83, wherein the reader device is an infrastructure equipment of the wireless communications network, and wherein the one or more other devices comprise one or more communications devices.

[0221] 85. The method according to any of clauses 43-83, wherein the reader device is a communications device, and wherein the one or more other devices comprise an infrastructure equipment of the wireless communications network.

[0222] 86. The method according to any of clauses 43-85, wherein the communications device is of a first type, wherein the first type of communications device is one of a plurality of types of communications device configured to communicate with the wireless communications network, and the first type of communications device has a reduced hardware complexity compared with at least one other type of communications device of the plurality of types of communications device.

[0223] 87. The method according to clause 86, wherein the at least one other type of communications device is a mobile phone.

[0224] 88. The method according to any of clauses 43-87, wherein communications device is an internet-of-things (loT) device.

[0225] 89. The method according to clause 88, wherein the loT device is an ambient loT device.

[0226] 90. The method according to any of clauses 43-89, wherein the communications device is a Machine-Type-Communication (MTC) device. 91. The method according to any of clauses 43-90, wherein the communications device has no Radio Resource Control (RRC) state with the wireless communications network.

[0227] 92. A communications device, the communications device comprising: transceiver circuitry configured to transmit signals to and / or to receive signals from an infrastructure equipment of a wireless communications network via a radio access interface between the communications device and the infrastructure equipment, and controller circuitry configured in combination with the transceiver circuitry to: receiving a reader-to-device (R2D) signal from a reader device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of a radio access interface of the wireless communications network, wherein the R2D signal corresponds to an ON- OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device, a tail portion located at an end of the OFDM symbol, and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information; detecting the CP and tail portion to identify the additional information; and identifying the first data.

[0228] 93. Circuitry for a communications device, the circuitry comprising: transceiver circuitry configured to transmit signals to and / or to receive signals from an infrastructure equipment of a wireless communications network via a radio access interface between the communications device and the infrastructure equipment, and controller circuitry configured in combination with the transceiver circuitry to: receiving a reader-to-device (R2D) signal from a reader device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of a radio access interface of the wireless communications network, wherein the R2D signal corresponds to an ON- OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device, a tail portion located at an end of the OFDM symbol, and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information; detecting the CP and tail portion to identify the additional information; and identifying the first data. REFERENCES

[0229] [1] RP-234058, “New SID: Study on solutions for Ambient loT (Internet of Things) in NR”. RAN plenary #102. Edinburgh. December 2023.

[0230] [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.

[0231] [3] TR38.848. “Study on Ambient loT (Internet of Things) in RAN”, 3GPP.

[0232] [4] Van Huynh, Nguyen, Dinh Thai Hoang, Xiao Lu, Dusit Niyato, Ping Wang, and Dong In Kim. "Ambient Backscatter Communications: A Contemporary Survey." IEEE Communications Surveys & Tutorials 20, no. 4 (2018): 2889-2922.

[0233] [5] RP-234065, “New WID: Enhancements of network energy savings for NR,” 3GPP TSG RAN Meeting#102, Edinburgh, Scotland, December 11 th-15th, 2023

[0234] [6] GSMA, 5G energy efficiencies: Green is the new black, https: / / data.gsmaintelligence.com / api-web / v2 / research-file- download?id=54165956&file=241120-5G-energy.pdf

[0235] [7] R1-2403821 “Report of RAN1#116bis meeting”. ETSI MC, 3GPP TSG RAN WG1 #117, Fukuoka, Japan, May 20th - May 24th, 2024.

[0236] [8] ‘Draft Report of 3GPP TSG RAN WG1 #117 v0.2.0’, 3GPP TSG RAN WG1 #117, Fukuoka, Japan, May 20th - May 24th, 2024.

Claims

CLAIMS1 . A method of operating a reader device forming part of a wireless communications network and configured to transmit signals to and / or to receive signals from one or more other devices of the wireless communications network via a radio access interface between the reader device and the one or more other devices, the method comprising: transmitting a reader-to-device (R2D) signal for receipt by a communications device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of the radio access interface, wherein the R2D signal is transmitted according to an ON- OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device; a tail portion located at an end of the OFDM symbol; and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information for receipt by the communication’s device.

2. The method according to claim 1 , wherein the second signal is a predetermined synchronisation signal, and wherein the additional information is a clock timing.

3. The method according to claim 1 , wherein the second signal is an ON signal.

4. The method according to claim 1 , wherein the second signal is an OFF signal.

5. The method according to claim 1 , wherein the second signal is a signal with one or more amplitude transitions between an ON signal and an OFF signal.

6. The method according to claim 5, wherein the second signal is an ON signal which transitions to an OFF signal.

7. The method according of claim 5, wherein the second signal is an OFF signal which transitions to an ON signal.

8. The method according to claim 5, wherein the second signal is a signal with a plurality of amplitude transitions between an ON signal and an OFF signal.

9. The method according to claim 1 , wherein the additional information is second data for receipt by the communications device, and wherein the second signal is based on the second data.

10. The method according to claim 9, wherein the second data is a 0 bit value or a 1 bit value, and wherein the second signal indicates either the 0 bit value or the 1 bit value.

11. The method according to claim 9, wherein the second data indicated by the second signal is based on the first data included in the data portion.

12. The method according to claim 11 , wherein the second data indicated by the second signal is a parity bit having a value set according to the first data and a parity system.

13. The method according to claim 12, wherein the parity system is a bit-level parity system, and wherein the parity bit has a value set according to one or more bits included in the first data.

14. The method according to claim 12, wherein the parity system is a chip-level parity system, and wherein the parity bit has a value set according to one or more ON signals and / or one or more OFF signals included in the first signal.

15. The method according to any of claims 9-14, wherein the second data is indicative of the first data indicated by the first signal.

16. The method according to claim 9, wherein the second signal is repeated in one or more subsequent OFDM symbols.

17. The method according to claim 1 , wherein the second signal is an OFF signal or an ON signal, and wherein the second signal is an extension of a final chip of a plurality of chips making up the data portion.

18. The method according to claim 17, wherein a length of the plurality of chips is set such that a length of the final chip plus the tail portion is equal to a length of each of the remaining chips of the plurality of chips of the data portion.

19. The method according to claim 17, wherein a length of the plurality of chips is set such that a length of the final chip plus the CP and tail portion is equal to a length of each of the remaining chips of the plurality of chips of the data portion.

20. The method according to claim 1 , wherein the second signal is an OFF signal or an ON signal, and wherein the second signal is an early extension of an initial chip of a plurality of chips making up the data portion.

21. The method according to claim 20, wherein a length of the plurality of chips is set such that a length of the initial chip plus the CP is equal to a length of each of the remaining chips of the plurality of chips of the data portion.

22. The method according to claim 20, wherein a length of the plurality of chips is set such that a length of the initial chip plus the CP and tail portion is equal to a length of each of the remaining chips of the plurality of chips of the data portion.

23. The method according to claim 1 , wherein an end of the second signal of the tail portion is contiguous with a start of a CP of a next OFDM symbol.

24. The method according to claim 1 , wherein an amplitude of an ON signal of the second signal has a higher amplitude than an amplitude of an ON signal of the first signal.

25. The method according to claim 24, wherein the amplitude of the ON signal of the second signal is indicated in specifications.

26. The method according to claim 24, wherein the amplitude of the ON signal of the second signal is indicated in a preamble of the R2D signal.

27. The method according to claim 24, further comprising: transmitting, to the communications device and separate prior to the R2D signal, an indication of the amplitude of the ON signal of the second signal.

28. The method according to claim 27, wherein the indication of the amplitude of the ON signal of the second signal is included in a system information block (SIB).

29. The method according to claim 1 , wherein the first signal is Manchester-encoded.

30. The method according to claim 1, wherein the first data comprises one or more bits.

31. The method according to claim 1 , wherein the reader device is an infrastructure equipment of the wireless communications network, and wherein the one or more other devices comprise one or more communications devices.

32. The method according to claim 1, wherein the reader device is a communications device, and wherein the one or more other devices comprise an infrastructure equipment of the wireless communications network.

33. The method according to claim 1, wherein the communications device is of a first type, wherein the first type of communications device is one of a plurality of types of communications device configured to communicate with the wireless communications network, and the first type of communications device has a reduced hardware complexity compared with at least one other type of communications device of the plurality of types of communications device.

34. The method according to claim 33, wherein the at least one other type of communications device is a mobile phone.

35. The method according to claim 1, wherein the communications device is an internet-of- things (loT) device.

36. The method according to claim 35, wherein the loT device is an ambient loT device.

37. The method according to claim 1 , wherein the communications device is a Machine-Type- Communication (MTC) device.

38. The method according to claim 1, wherein the communications device has no Radio Resource Control (RRC) state with the wireless communications network.

39. The method according to claim 1, wherein transmitting the R2D signal comprises generating the R2D signal for transmission using the OOK structure.

40. The method according to claim 39, wherein generating the R2D signal for transmission using the OOK structure comprises: determining the OOK structure comprising the data portion and the tail portion;performing a fast Fourier transform on the OOK structure to obtain a frequency-domain signal; performing one or more modifications to the frequency-domain signal; performing an inverse fast Fourier transform on the modified frequency-domain signal to obtain a time-domain signal comprising the data portion and the tail portion; adding the CP to the time-domain signal by duplicating the tail portion to precede the data portion, to obtain the R2D signal for transmission.

41. A reader device configured to form part of a wireless communications network, the reader device comprising: transceiver circuitry configured to transmit signals to and / or to receive signals from one or more other devices of the wireless communications network via a radio access interface between the reader device and the one or more other devices, and controller circuitry, the transceiver and controller circuitry configured to, in combination: transmitting a reader-to-device (R2D) signal for receipt by a communications device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of the radio access interface, wherein the R2D signal is transmitted according to an ON-OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device; a tail portion located at an end of the OFDM symbol; and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information for receipt by the communication’s device.

42. Circuitry for a reader device configured to form part of a wireless communications network, the reader device comprising: transceiver circuitry configured to transmit signals to and / or to receive signals from one or more other devices of the wireless communications network via a radio access interface between the reader device and the one or more other devices, and controller circuitry, the transceiver and controller circuitry configured to, in combination: transmitting a reader-to-device (R2D) signal for receipt by a communications device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of the radio access interface, wherein the R2D signal is transmitted according to an ON-OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises:a data portion comprising a first signal indicative of first data for receipt by the communications device; a tail portion located at an end of the OFDM symbol; and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information for receipt by the communication’s device.

43. A method of operating a communications device configured to transmit signals to and / or to receive signals from a reader device of a wireless communications network, the method comprising: receiving a reader-to-device (R2D) signal from a reader device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of a radio access interface of the wireless communications network, wherein the R2D signal corresponds to an ON- OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device, a tail portion located at an end of the OFDM symbol, and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information; detecting the CP and tail portion to identify the additional information; and identifying the first data.

44. The method according to claim 43, wherein the communications device detects the CP and tail portion using a correlation method.

45. The method according to claim 44, wherein the correlation method comprises an autocorrelation method which samples the R2D signal to identify the CP and tail portion.

46. The method according to claim 45, wherein the autocorrelation method comprises comparing correlation values for a plurality of sample counts for one or more OFDM symbols of the R2D signal.

47. The method according to claim 45, wherein the autocorrelation method comprises identifying a location of the tail portion based on an identified correlation between the R2D signal and the second signal of the CP.

48. The method according to claim 43, wherein correlation method comprises correlating the R2D signal according to a clock of the communications device to identify the CP and tail portion.

49. The method according to claim 44, wherein the correlation method comprises correlating the R2D signal with a predetermined signal pattern for the CP and tail portion.

50. The method according to claim 44, wherein the correlation method is performed separately for a plurality of blocks of OFDM symbols of the R2D signal, wherein the blocks of OFDM symbols are each a subset of the OFDM symbols of the R2D signal.

51. The method according to claim 44, wherein the correlation method is performed collectively for the entirety of the R2D signal.

52. The method according to claim 43, further comprising: adjusting a clock timing for the communications device according to the detected CP and tail portion.

53. The method according to claim 43, further comprising: estimating a sampling frequency offset of the communications device based on a timing of the detected CP and tail portion.

54. The method according to claim 53, wherein estimating the sampling frequency offset is based on comparing a detected number of samples forming the data portion with a predetermined number of samples for the data portion.

55. The method according to claim 54, wherein the predetermined number of samples is determined based on a chip length for the OOK structure and a total number of chips in the OFDM symbol.

56. The method according to claim 55, wherein the chip length and the total number of chips is either: defined in specifications, or received by the communications device in signalling from the wireless communications network.

57. The method according to claim 53, further comprising:adjusting the sampling frequency of the communications device according to the estimated sampling frequency offset.

58. The method according to claim 43, wherein each OFDM symbol of the R2D is formed of a plurality of chips, wherein the preamble of the R2D signal indicates a total number of chips of the R2D signal, and / or a duration of each of the plurality of chips.

59. The method according to claim 58, wherein the total number of chips and / or the chip duration is indicated by a preamble of the R2D signal.

60. The method according to claim 58, wherein an indication of the total number of chips and / or the chip duration is received from the reader device in signalling separate from the R2D signal.

61. The method according to claim 58, wherein the total number of chips and / or the chip duration is defined in specifications.

62. The method according to claim 43, wherein the additional information is second data, and wherein the second signal is based on the second data.

63. The method according to claim 62, wherein the second data is indicative of the first data, and wherein the identifying the first data is based on the identified second data.

64. The method according to claim 63, wherein identifying the first data is based on assigning a first weighting to the received first signal and a second weighting to the received second signal according to the respective robustness of the first signal and the second signal.

65. The method according to claim 64, wherein the second weighting is set to a higher value based on an amplitude of an ON signal of the second signal being higher amplitude than an amplitude of an ON signal of the first signal.

66. The method according to claim 64, wherein the second weighting is set to a higher value based on an end of the second signal of the tail portion being contiguous with a start of a CP of a next OFDM symbol.

67. The method according to claim 62, wherein the second data indicated by the second signal is a parity bit having a value set according to the first data and a parity system, and whereinidentifying the first data is based on performing a parity check according to the parity system using the parity bit.

68. The method according to claim 67, wherein the parity system is a bit-level parity system, and wherein the parity bit has a value set according to one or more bits included in the first data.

69. The method according to claim 67, wherein the parity system is a chip-level parity system, and wherein the parity bit has a value set according to one or more ON signals and / or one or more OFF signals included in the first signal.

70. The method according to claim 43, wherein the second signal is a predetermined signal pattern.

71. The method according to claim 43, wherein the second signal is an ON signal.

72. The method according to claim 43, wherein the second signal is an OFF signal.

73. The method according to claim 43, wherein the second signal is a signal with one or more amplitude transitions between an ON signal and an OFF signal.

74. The method according to claim 73, wherein the second signal is an ON signal which transitions to an OFF signal.

75. The method according of claim 73, wherein the second signal is an OFF signal which transitions to an ON signal.

76. The method according to claim 73, wherein the second signal is a signal with a plurality of amplitude transitions between an ON signal and an OFF signal.

77. The method according to claim 43, wherein the second signal is an OFF signal or an ON signal, and wherein the second signal is an extension of a final chip of a plurality of chips making up the data portion.

78. The method according to claim 77, wherein a length of the plurality of chips is set such that a length of the final chip plus the tail portion is equal to a length of each of the remaining chips of the plurality of chips of the data portion.

79. The method according to claim 77, wherein a length of the plurality of chips is set such that a length of the final chip plus the CP and tail portion equal to a length of each of the remaining chips of the plurality of chips of the data portion.

80. The method according to claim 43, wherein the second signal is an OFF signal or an ON signal, and wherein the second signal is an early extension of an initial chip of a plurality of chips making up the data portion.

81. The method according to claim 80, wherein a length of the plurality of chips is set such that a length of the initial chip plus the CP is equal to a length of each of the remaining chips of the plurality of chips of the data portion.

82. The method according to claim 80, wherein a length of the plurality of chips is set such that a length of the initial chip plus the CP and tail portion is equal to a length of each of the remaining chips of the plurality of chips of the data portion.

83. The method according to claim 43, wherein an end of the second signal of the tail portion is contiguous with a start of a CP of a next OFDM symbol.

84. The method according to claim 43, wherein the reader device is an infrastructure equipment of the wireless communications network, and wherein the one or more other devices comprise one or more communications devices.

85. The method according to claim 43, wherein the reader device is a communications device, and wherein the one or more other devices comprise an infrastructure equipment of the wireless communications network.

86. The method according to claim 43, wherein the communications device is of a first type, wherein the first type of communications device is one of a plurality of types of communications device configured to communicate with the wireless communications network, and the first type of communications device has a reduced hardware complexity compared with at least one other type of communications device of the plurality of types of communications device.

87. The method according to claim 86, wherein the at least one other type of communications device is a mobile phone.

88. The method according to claim 43, wherein communications device is an internet-of-things (loT) device.

89. The method according to claim 88, wherein the loT device is an ambient loT device.

90. The method according to claim 43, wherein the communications device is a Machine- Type-Communication (MTC) device.

91. The method according to claim 43, wherein the communications device has no Radio Resource Control (RRC) state with the wireless communications network.

92. A communications device, the communications device comprising: transceiver circuitry configured to transmit signals to and / or to receive signals from an infrastructure equipment of a wireless communications network via a radio access interface between the communications device and the infrastructure equipment, and controller circuitry configured in combination with the transceiver circuitry to: receiving a reader-to-device (R2D) signal from a reader device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols of a radio access interface of the wireless communications network, wherein the R2D signal corresponds to an ON-OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device, a tail portion located at an end of the OFDM symbol, and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information; detecting the CP and tail portion to identify the additional information; and identifying the first data.

93. Circuitry for a communications device, the circuitry comprising: transceiver circuitry configured to transmit signals to and / or to receive signals from an infrastructure equipment of a wireless communications network via a radio access interface between the communications device and the infrastructure equipment, and controller circuitry configured in combination with the transceiver circuitry to: receiving a reader-to-device (R2D) signal from a reader device, wherein the R2D signal spans one or more orthogonal frequency-division multiplexing (OFDM) symbols ofa radio access interface of the wireless communications network, wherein the R2D signal corresponds to an ON-OFF-keying (OOK) structure, wherein the OOK structure for each of the one or more OFDM symbols comprises: a data portion comprising a first signal indicative of first data for receipt by the communications device, a tail portion located at an end of the OFDM symbol, and a cyclic prefix (CP) located at the start of the OFDM symbol, wherein the CP is a duplicate of the tail portion, and wherein the tail portion and the CP each comprise a second signal indicative of additional information; detecting the CP and tail portion to identify the additional information; and identifying the first data.

Images