Methods, communications apparatus and devices

Abstract

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 low power devices such as AIoT

Description

BACKGROUND Field of the Disclosure The present disclosure relates to methods, a communications apparatus and devices. Background 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. Current and future wireless communications networks are expected routinely and efficiently to support communications with an ever-increasing range of devices associated with a wider range of data traffic profiles and types. For example, wireless communications networks will be expected efficiently to support communications with devices including reduced complexity devices, machine type communication (MTC) devices, high resolution video displays, virtual reality headsets, extended Reality (XR) and so on. Some of these different types of devices may be deployed in very large numbers, for example low complexity devices for supporting the “The Internet of Things”, and may typically be associated with the transmissions of relatively small amounts of data with relatively high latency tolerance. Other types of device, for example, devices 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 devices used for autonomous vehicle communications and for other critical applications, may be characterised by data that should be transmitted through the network with low latency and high reliability. A single device type might also be associated with different traffic profiles / characteristics depending on the application(s) it is running. For example, different considerations may apply for efficiently supporting data exchange with a smartphone when it is running a video streaming application (high downlink data) as compared to when it is running an Internet browsing application (sporadic uplink and downlink data) or being used for voice communications by an emergency responder in an emergency scenario (data subject to stringent reliability and latency requirements). In view of this there is expected to be a desire for current wireless communications networks, for example those which may be referred to as 5G or new radio (NR) systems / new radio access technology (RAT) systems, or indeed future 6G wireless communications, as well as future iterations / releases of existing systems, efficiently to support connectivity for a wide range of devices associated with different applications and different characteristic data traffic profiles and requirements. 5G NR has continuously evolved and the current work plan includes 5G-NR-Advanced in which some further enhancements are expected, especially to support new use-cases / scenarios with higher requirements. A further area of study which has developed concerns the use of low complexity devices, which may use power from incident radiation for communicating or backscattering received signals. Such devices may be referred to as tags or Ambient loT devices (tags / A-IoT). Improving communication with such devices can represent a technical challenge. SUMMARY The present disclosure can help address or mitigate at least some of the issues discussed above. According to example embodiments a communications device acting as a reader for a low power or ultra low power device, such as an A-IoT device or 6G loT device, and a method of operating a reader device for a low power device or an ultra low power device is disclosed. The reader forms part of a wireless communications network and is configured to transmit signals to and / or to receive signals from one or more other low power devices via a radio access interface between the reader device and the one or more other low power devices. The method comprises receiving an initial access signal from a first low power device among the one or more low power devices on first resources randomly selected by the first low power device according to a contentious access procedure; associating the first resources to the first low power device; and transmitting a R2D signal to the first low power device indicating a successful receipt of the initial access signal. According to various disclosed examples, the method can provide an energy efficient contention based channel access signaling method for A-IoT devices to access the channel resources. Respective aspects and features of the present disclosure are defined in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the present technology. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS 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: Figures 1A and IB schematically represent examples of communications systems in which A-IoT devices 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; Figures 2A and 2B schematically represent examples in which a reader in the form of a base station of a wireless communications network (Figure 2A) and a communications device (UE) of a wireless communications network (Figure 2B) transmit a reader to device (R2D) signal to a A-IoT device and receive a response signal as a backscattered signal according to example embodiments; Figure 3 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; Figure 4 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; Figure 5 is a schematic block diagram illustrating an example of backscattering circuitry of an example A-IoT device; Figure 6 is a schematic illustration representing an example in which a carrier wave signal transmitted by an external carrier wave emitter is backscattered; Figure 7 is an illustrative representation of channel access based on slotted ALOHA scheme with resources in time domain; Figure 8 is an illustrative representation of a contention based channel access mechanism for accessing D2R resources in accordance with embodiments of the present disclosure; Figure 9 is an activity chart representation illustrating the process of a A-IoT device selecting resources for initial access and keeping a semi-persistent scheduling in accordance with embodiments of the present disclosure; Figure 10 is an illustrative representation of a contention based channel access mechanism for accessing D2R and R2D resources in accordance with embodiments of the present disclosure; Figure 11 is an activity chart representation illustrating the process of a reader device monitoring for resource usage and using resources in accordance with embodiments of the present disclosure; Figure 12 illustrates a signal flow diagram representation of an example communications system comprising A-IoT devices, reader devices and an infrastructure equipment in accordance with embodiments of the present disclosure; Figure 13 is a flow diagram illustrating 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 A-IoT devices in accordance with example embodiments of the present disclosure; and Figure 14 is a flow diagram illustrating a method of operating an A-IoT device configured to transmit signals to and / or to receive signals from reader devices forming part of a wireless communications network in accordance with example embodiments of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS Ambient loT In release 19 of 3GPP (Rei-19), 3GPP will study Ambient loT [1] where a communications device (such as a user equipment (UE)) is essentially a communications device with very limited energy consumption in range of 1 pW to several hundreds of pW. In Ambient loT, it is considered that the communications device may harvest energy to power its communication with a base station (such as a gNB). For example, the energy may be harvested from solar or kinetic energy such as vibrations. Alternatively, the energy to power the communications device may 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 communications devices are powered by radio frequency energy derived from radio signals transmitted as a carrier wave (CW) by a CWE is shown in 3 Figures 1A and IB. Figures 1A and IB 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. The tags 1 may also be referred to as ambient loT (A-IoT) devices. In the present disclosure, the terms ‘tag’ and ‘ A-IoT device may be used interchangeably except where indicated otherwise. 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. In a second example, a UE 7 receives a backscattered signal 5 or an RF signal generated by the tags from the tags 1. The UE 7 then transmits an indication of the received 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 received signals are detected by the detection station (UE) 7, and the detection station transmits an indication of the detected received signals to the gNB 4. The station which controls the CWEs 3 may be regarded as a controller station. The station which detects the received 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 IB the detection station 7 in the form of the UE is separate from the gNB 4 which acts as a controller station. According to the arrangements of Figures 1A and IB, 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. As shown in Figures 1A and IB, 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. 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 A-IoT device to transmit data in the uplink by backscattering another signal (for example the DL signal from the gNB 4). In some examples, such as the example of Figure IB, 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 3 and 4. 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. Although Figures 1A and IB describe A-IoT devices performing data transmission based on backscattered signals, the present disclosure is not so limited and any low power or ultra-low power devices generating its own RF signal are also envisaged. Figures 2A and 2B provide alternative scenarios in which a reader of a tag / A-IoT device 1 transmits a reader to device (R2D) signal 21 to the tag / A-IoT device 1. In Figure 2A, the reader is a gNB 4 and in Figure 2B the reader is a UE 7. In some examples the reader may also receive a backscattered signal 5 reflected or backscattered by the tag / A-IoT device 1. Example embodiments described below relate to a design of the R2D signal 21. A problem addressed by the present technique concerns a need for the tags to synchronise with information transmitted in the R2D signal. The tags / A-IoT devices 1 may be of low complexity and have low accuracy clocks in order to reduce device complexity and to reduce 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. The low complexity of the tag / A-IoT device means that there may be limited processing capability for both cost and power consumption reasons and it is likely to be challenging to maintain an accurate clock frequency. The sampling frequency offset (SFO) can reach 104 or 105 parts per million (ppm) and can depend on device type. A type 1 device is a very low cost, low power and low complexity device and may use a ring oscillator with a frequency accuracy of 105 parts per million (ppm). In contrast, a type 2a or 2b device can tolerate higher cost, higher power consumption and higher complexity. These type 2a or 2b devices may use an RC or crystal oscillator having a frequency accuracy of 103 or 104 parts per million (ppm). The frequency accuracy impacts the SFO directly. It is hence apparent that the initial SFO may relate to the device type. The SFO of a device can alternatively be determined by a reader from a measurement performed by the reader during a protocol exchange involving D2R signals that are sent by the tag / A-IoT device. In this case, the reader can measure the SFO on the D2R signals and determine that that SFO will also be applied by the tag / A-IoT device when the tag / A-IoT device decoding R2D signals. A tag / A-IoT device will have a small energy store; hence reception and transmission procedures can only consume small amounts of power. The device may hence not be capable of performing complicated signal processing algorithms. Although Figures 2A and 2B describe A-IoT devices performing data transmission based on backscattered signals, the present disclosure is not so limited and any low power or ultra-low power devices generating its own RF signal are also envisaged. 5G New Radio (NR) Wireless Communications System As indicated above, example embodiments utilise and / or form part of components of the wireless communications network as illustrated in Figures 1A and IB and 2A and 2B. An example configuration of a wireless communications network which uses some of the terminology proposed for NR is shown in Figure 3. In Figure 3 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 7, 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. The elements of the wireless access network shown in Figure 3 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 3 and of other networks discussed herein in accordance with embodiments of the disclosure which are not specifically described (for example in relation to specific communication protocols and physical channels for communicating between different elements) may be implemented in accordance with any known techniques, for example according to currently used approaches for implementing such operational aspects of wireless telecommunications systems, e.g. in accordance with the relevant standards. The TRPs 10 of Figure 3 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. The term network infrastructure equipment / 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 6 and / or TRPs 10. Communications devices 7 are represented in Figure 3 within the coverage area of respective communication cells 12. These communications devices 7 may thus exchange signalling with the CU 40 via the TRP 10 associated with their respective communications cells 12. It will further be appreciated that Figure 3 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. A more detailed diagram of some of the components of the network shown in Figure 3 is provided by Figure 4. In Figure 4, a TRP 10 as shown in Figure 3 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 7 within a cell 12 formed by the TRP 10. As shown in Figure 4, an example UE 7 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. The transmitters 30, 49 and the receivers 32, 48 (as well as other transmitters, receivers and transceivers described in relation to examples and embodiments of the present disclosure) may include radio frequency filters and amplifiers as well as signal processing components and devices in order to transmit and receive radio signals in accordance, for example, with the 5G / NR standard. The controllers 34, 44 (as well as other controllers described in relation to examples and embodiments of the present disclosure) may be, for example, a microprocessor, a CPU, or a dedicated chipset, etc., configured to carry out instructions which are stored on a computer readable medium, such as a non-volatile memory. The processing steps described herein may be carried out by, for example, a microprocessor in conjunction with a random access memory, operating according to instructions stored on a computer readable medium. The interface 46 between the DU 42 and the CU 40 is known as the Fl interface which can be a physical or a logical interface. The Fl 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 TRP 10 to the DU 42 and the Fl interface 46 from the DU 42 to the CU 40. RF Incident Energy As explained above with reference to the example shown in Figures 1 A, IB, 2A and 2B, Ambient loT proposes to use energy received from a radio frequency carrier wave in order to power devices. An Ambient loT device 1 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. Backscattering Principle As explained above with reference to Figures 1 A, IB, 2A and 2B, 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. 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 5 illustrates a generic form of the backscattering circuitry including a matching network and an integrated circuit (IC). There are two aspects of power that are relevant to the Ambient loT device: • Absorbed power. This is the power that is energy harvested and can be used to drive the circuits within the tag. • Reflected power. This is the power that is reflected as a backscattered signal. Given the antenna and load impedances denoted as Za = Ra + jXa and Za = Rn + jXn, n = 1,2, respectively, the reflection coefficient corresponding to each state is expressed as Zn-z: •p __ n d n — 7 + Z where * denotes the complex conjugate operation. Note that Figure 5 shows the antenna impedance Za as Zant. 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*a, F, = 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 Zn that is much greater than Za will lead to a reflection coefficient close to 1, leading to a higher reflection state. Note that in practice, the reflection coefficient |Fn | depends on the manufacturing process and may vary within the range of (0,1). The absorbed power can be calculated as ^in,n = ^avail(l “ 1^(2) where Pavail denotes 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: = i - |rn|2 4RnRa \zn+za\2 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. Given Pavau, the average power absorbed by the device can be calculated as Pin = PavaH (Pl(l ~ ^112) + P2(l ~ IT2 |2)) Where pn,n=i,2 denote the ratio of time duration for each impedance state; p± = p2 holds if the probability of each impedance equals to the other (this also means that the same probability of Os and Is appears in the encoded data if the backscattered signal uses a pure OOK waveform). CW Emitter As explained above with reference to Figures 1 A, IB, 2A and 2B, carrier-wave emitters (or CW emitter / CWE) can transmit a carrier wave signal (CWS) that can be used by the tag to backscatter a signal from. As explained above, the CWE may form part of a reader or detector and the CWS may be the R2D signal transmitted by the reader. 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 6. Figure 6 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 5. 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. More explanation of the role and functionality of the CWE and CWS is described in European patent application 24192725.0, the contents of which are incorporated herein by reference. Although embodiments of the present disclosure describe A-IoT devices performing data transmission based on backscattered signals, it is envisaged that the various concepts of uplink contention free channel access described herein may be equally employed for other types of low power or ultra-low power devices that generate its own RF signals. A-IoT uplink contention based channel access with reduced overhead As discussed above, to meet design targets and use cases where existing 3GPP LPWA loT solution are not able to compete, 3GPP study has been carried out targeting to standardize a system for connecting ultra-low power and / or ultra-low complexity A-IoT devices in cellular networks. In terms of energy storage, the study considers two main types of device characteristics. The first type is an extremely low energy storage limited device, capable of consuming only 1 pW in peak power consumption. The second type has more energy storage and aims to support power consumption less than a few hundred pW. Both the first type and the second type A-IoT devices may have their uplinks based on backscattering transmission. The second type of A-IoT devices may also conduct their own uplink transmission in a conventional way. In order for these A-IoT devices to access the channel resources, methods consuming very low amount of energy are required. Embodiments of the present technique provides a contention-based channel access scheme with low protocol overhead, allowing resource selection for both D2R (uplink) and the associated R2D (downlink) transmissions. In addition, it has been set out that the objective of the 3GPP study for item Ambient loT (Revised SID, RP-240826) concerns light weight signalling procedures enabling Device Originated - Device Terminated Triggered (DO-DTT) and Device Terminated (DT) data transmission. DO-DTT data transmission is intended for uplink, i.e. D2R transmissions that are triggered / controlled from network side. DT data transmission is intended for sending DL / R2D command to the A-IoT devices. Embodiments of the present technique mainly focus on the case of DO-DTT data transmission. Given the 3GPP work so far, it is expected to have a control information (R2D) to be provided to the A-IoT device. There may be two types of R2D control signals: i) an inventory, triggering many devices at the same time without including any device address or ID, or ii) a triggering command which may need to also be followed by data information including devices group address or ID. This means, in both cases, many devices may need to access the channel at the same time. In A-IoT energy is considered to be constrained. The interval between a R2D control information reception and a subsequent D2R transmission may depend on different factors, e.g., the amount of available energy at the A-IoT device, the clock accuracy and synchronization status of the A-IoT device. Furthermore, it has been discussed how an A-IoT device initially accesses the channel resources after receiving the (first) R2D triggering message. The two known methods are contention based and contention free channel access. The former may lead to a collision while the latter is done based on scheduling and therefore there is no collision. In the 3GPP legacy methods, the initial access is referred to as a sequence of processes between UE and Network for a UE to acquire uplink synchronization and obtain specified identity for the radio access communication. This can be done in a 2-step and 4-step Random Access Channel (RACH) procedure. Both RACH configuration and its procedure may become very energy costly for A-IoT devices with limited energy resources. Therefore, there is a need for an improved channel access schemes suitable for energy constrained A-IoT devices. Embodiments of the present disclosure mainly focus on energy efficient contention-based channel access method for A-IoT devices. Slotted ALOHA is a known contention-based channel access widely used in wireless sensor type applications. This scheme has also been proposed to be studied as part of the SI for A-IoT in 3GPP. In slotted ALOHA, the channel time is separated into time slots. The device attempts to transmit payload data at a certain slot. Similarly, the slotted ALOHA concept can be extended also in frequency domain, but the method still would be the same. Both concepts may be combined with a feedback / acknowledgement mechanism where any success of the channel access is communicated. For example, RFID (often provided as examples in 3GPP discussions) system uses a slotted aloha. While slotted ALOHA reduces channel access collision, there is a certain probability that two devices access the channel at the same time. Figure 7 shows an illustrative representation of channel access based on slotted ALOHA scheme with resources in time domain. In Figure 7, device 1 and device 2 attempt to transmit data at the beginning of the discrete time slots. Upon resource collision between device 1 and device 2 occurs at time slots S3, device 1 makes a new attempt at slot S5 after a two-slot delay, whereas device 2 makes a new attempt at slot S8 after a five-slot delay. Resource collision is reduced for the second attempts because the slot delay for each device is randomly determined. Reservation based slotted ALOHA is also a known mechanism that exploits a trial-and-error reservation mechanism or allocation. When a device succeeds with a transmission trying out on random slot, that particular slot is kept “assigned” to the device during transmission of a message. The reservation based slotted aloha has been shown superior to slotted aloha in particular at cases where longer packages are fragmented over multiple slots. The 3GPP study on A-IoT technology and some initial design targets, requirements, topologies, deployment scenarios, etc., are discussed in a technical report TR38.848 and TR38.769. There are also extensive ongoing discussions of the topic in RANI 3GPP agenda Item 9.4.2.2. Specifically, a summary of the latest discussions for random access is set out in section 4 of Rl-2409244

[13] , The present disclosure can help address or mitigate at least some of the issues discussed above, by providing an energy efficient contention-based channel access method for A-IoT devices for both D2R and R2D transmissions with minimum protocol overhead. Embodiments of the present disclosure are based upon the slotted aloha / framed slotted aloha concept with improvements and adaptation to meet the need of A-IoT. Embodiments of the present technique provides a contention-based mechanism for A-IoT devices to access the channel. The contention-based mechanism comprises the reader device receiving an initial access signal from an A-IoT device. The initial access signal requests channel access for communicating on first resources randomly selected by the A-IoT device according to a contentious access procedure. Next the reader device associates the selected resources to the A-loT device, and transmits an acknowledge signal to the A-IoT device indicating a successful channel access request attempt. Subsequently, the reader device and the A-IoT device perform data transmission via the selected resources. In some embodiments, before the A-IoT device transmits the initial access signal, the reader device may send an initial triggering R2D signal to provide time and frequency references referring to start and end, or a start frequency and time point together with time and frequency window, for contentious access. This information may be included in an individual R2D control signal or data part of a R2D data signal. This initial triggering R2D signal is particularly needed for DTT-DO scenarios. According to embodiments of the present technique, from the resources indicated by the R2D signal, the A-IoT device may initially access the D2R channel based on a randomized attempt similar to the slotted ALOHA / framed slotted aloha protocol. The A-IoT device then transmits its D2R signal containing its own identity. In some embodiments, the identity of the A-IoT device may be implicitly indicated in a D2R message or the like, so that is possible for the reader device to decode the message encoded by a particular A-IoT device. In some embodiments, the D2R signal may also contain the selected slot number and the reader’s identity, and may as well include a preamble and data part. The preamble is transmitted to indicate the start of the D2R transmission and used also for synchronization purposes. After reception of the D2R signal, the reader / network can calculate the resource / slot that the A-IoT device has selected for channel access. According to embodiments of the present technique, if the reader manages to receive and decode the information sent on the D2R channel, it will “semi-persistently” store and associate these resources as D2R resources to the A-IoT device. The A-IoT device may then transmit, any subsequent D2R signals, related to the same R2D triggering signal or a new triggering R2D signal, within these slots. According to some embodiments of the present technique, the reader may associate the D2R resource selection to R2D (e.g. by TDMA, or FDMA, or a reference time window of configuration) resources. Meanwhile, the A-IoT device performs the same association to the R2D signal and the reader device. As such, the A-IoT device only needs to listen on those R2D resources for the expected R2D signal (e.g. unicast resources) following its D2R transmission. According to some embodiments of the present technique, if there is an observed congestion (e.g. D2R data transmission is not acknowledged by the reader device), the A-IoT device may need to perform a new random selection of resources. The reader device or the network will also reassociate the newly selected resources according to a new physical resource request received from the A-IoT device. An advantage of such mechanism is reduced overhead compared to a contention-free based scheme. This is since the reader device does not need to transmit additional R2D triggering and scheduling signals, for scheduling D2R channel access of different A-IoT devices. In some embodiments, if the reader device is an intermediate node, it may also inform the network of the resource selection. Additionally or optionally, the reader device or the network may book keep the selected resources and determine potential resource conflicts between multiple reader devices. By allowing a resource space larger than the number of A-IoT devices accessing the channel, the collision probability can be further reduced. Under collision, the reader device or the network may transmit an R2D message, requesting the A-IoT devices to perform resource reselection, as will be further described below. Figure 8 is an illustrative representation of a contention based channel access mechanism for accessing D2R resources in accordance with embodiments of the present technique. In Figure 8, the A-IoT device DI at the second frame randomly selects the frequency and time resources (time slot TS2 and frequency slot FS2) and attempts to transmit an initial access signal at the selected physical resources. The reader device receives the initial access signal from the A-IoT device and detects the resource selection. Since the A-IoT device transmits the initial access signal with content of its identity, the reader device or the network can know what resources a particular A-loT device has selected for channel access. The reader device may then associate the same resources for further transmissions with the A-IoT device in subsequent reoccurring physical resources. The A-IoT device may therefore use the same resources for data transmission in reoccurring frames without any randomness. Figure 9 is an activity chart representation illustrating the process of a A-IoT device selecting resources for initial access and keeping a semi-persistent scheduling related to a successful channel access attempt in accordance with embodiments of the present technique. The process 900 begins at step 905, where the A-IoT device may receive an initial triggering signal from a reader device. The initial triggering signal may comprise time and frequency references for the A-IoT device to perform channel access according to a contentious access procedure, such as slotted ALOHA technique. In some embodiments, the initial triggering signal may be autonomously generated, for instance, by an application within the A-IoT device. At step 910, the A-IoT device randomly selects physical resources for channel access according to the contentious access procedure. The A-IoT device then uses the selected resources for transmitting an initial access signal to the reader device via the selected resources. The initial access signal requests channel access for communicating on the selected resources and may include an identity of the A-IoT device. The process the moves to steps 915 and 930, where the A-IoT device starts a timer and waits for the reader device to respond. At step 935, the A-IoT device checks whether a response is received from the reader device at the selected resources, that acknowledges the initial access signal and indicates a successful channel access request attempt. In the event that such response is received within a predetermined period of time, the process proceeds to steps 940 and 945, where the A-IoT device decodes the response from the reader device and configure the selected resources, which are now associated to the A-IoT device by the reader device, as semi-persistent resources for successive data transmission. Returning to step 935, in the event that a response is not received within a predetermined period of time, the process moves to step 910, where the A-IoT device determines that collision has occurred on the randomly selected resources, and performs a retransmission on the same reoccurring selected resources if the number of detected collisions is below a predetermined threshold. In some embodiments, the A-IoT device reselects random resources and performs a new channel access request attempt at the newly selected resources if the number of detected collisions is above a predetermined threshold. In some other embodiments, the A-IoT device may transmit a low overhead control message to the reader device upon detecting collision of data transmission, to allow the reader device to trigger a contention based resource reselection. In some other embodiments, the predetermined conditions for the reader device to trigger a contention based resource reselection may include detecting that no initial access signal is received by the first reader device for a predetermined time, which indicates congestion for transmitting A-IoT devices. Figure 10 is an illustrative representation of a contention based channel access mechanism for accessing D2R and R2D resources in accordance with embodiments of the present technique. According to some embodiments of the present technique, during D2R initial phase, the A-IoT device DI makes a channel access attempt on the selected frequency and time resources (time slot TS2 and frequency slot FS2) at the second frame. The A-IoT device successfully gets the D2R resource reservation as not collision occurs. At the same time, the A-IoT device is also associated to the R2D resource at time slot TS4 starting from the following frame. Figure 11 is an activity chart representation illustrating the process of a reader device monitoring for resource usage and using resources in accordance with embodiments of the present technique. The process 1100 commences at step 1105. Next, at step 1110, the reader device monitors for changes in the resources selected by the A-IoT devices. At step 1115, the reader device determines whether there is new resource usage by the A-IoT devices. This may be performed when a reader device needs to initiate a R2D data transmission with the A-IoT devices. In the event that there is new resource usage, the process proceeds to step 1120, where the reader device updates the association of resources by mapping the new resources to the relevant A-IoT devices. The process then moves to step 1125, where the reader device performs D2R / R2D transmission with the A-IoT devices according to updated resource association. Returning to step 1115, in the event that no new resource usage is detected, the process proceeds to step 1125, where the reader performs D2R / R2D transmission with the A-IoT devices according to the existing resource association. Signalling Figure 12 illustrates a signal flow diagram representation of an example communications system comprising A-IoT devices, reader devices and an infrastructure equipment performing contention based channel access method in accordance with embodiments of the present technique. Although Figure 12 shows that the reader device and the infrastructure equipment are separate devices, it is envisaged that the reader device and the infrastructure equipment may be the same device, and the signalling between reader device and the infrastructure equipment as described in Figure 12 may be internal signalling within the same device. In Figure 12, A-IoT device 1230 may firstly receive an initial triggering signal (not shown), for instance, from reader device 1220 or an application within the A-IoT device 1230. If the initial triggering signal is received from the reader device 1220, it may comprise time and frequency references for the A-IoT device 1230 to perform a contentious access procedure. Upon receiving the initial triggering signal, the A-IoT device 1230 randomly selects physical resources for channel access according to the contentious access procedure. In signal flow 1201, the A-IoT device 1230 transmits, to the reader device 1220, an initial access signal to request channel access for communicating on the randomly selected resources according to the contentious access procedure, such as slotted ALOHA technique. The reader device 1220 receives the initial access signal and decodes control information including an identifier of the A-IoT device 1230, and the resource selection made by A-IoT device 1230. The reader device 1220 then associates the randomly selected resources to the A-IoT device. Optionally or additionally, the reader device 1220 further forwards the control information from A-IoT device 1230 to an infrastructure equipment 1210 in the network, such as a gNB, via signal flow 1202, using legacy methods. Next, signal flow 1203 includes a request for response signal from the gNB 1210 to the reader device 1220. In signal flow 1204, the reader device 1220 sends an acknowledge signal to the A-IoT device 1230 indicating a successful channel access request attempt. Subsequently, the A-IoT device 1230 continues to use the selected resources for data transmission with the reader device 1220 via signal flow 1205. According to some embodiments of the present technique, an A-IoT device not expected to be always active in the selected resources. Therefore it is possible that multiple A-IoT devices can select the same resources causing only minimum congestion. In this case of congestion, a retransmission at the same reoccurring selected resources can be made by the A-IoT devices with a likely success rate. If the retransmission is considered unsuccessful, a new channel access attempt may be made at a random resources selected by the respective A-IoT devices. If still the network or reader device does not see it as sufficient, there could be a persisting problem with the selected resources causing congestions. The reader device may then trigger a new contention based “single” shot resource selection via a low overhead control message. This reselection features, would be relevant for cases where the reader device or network sees the current selection of resources causing repeated congestion, or the selection has been outdated, or when the selection of resource is not evenly distributed among the available resources. This reselection could be triggered for a single A-IoT device, a group of A-IoT devices, or all A-IoT devices. According to some embodiments of the present technique, to increase the scheduling space, the A-IoT devices may access the channel through CDMA-type channel access. In this case, more than one A-IoT device can access the same frequency and time resources at the same time. The above-described embodiments of the present technique concern a contention based channel access method with detection and association of resource selection. Specifically, the contention based channel access resources may be kept persistent for succeeding interaction. The D2R resources used at contention-based channel access may have an association / mapping to R2D resources. If more than one UE share same physical resources, they may be put in different groups for group cast, for example. Figure 13 shows a flow diagram illustrating 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 low power devices or ultra low power devices such as A-IoT devices in accordance with example embodiments of the present technique. The process shown by Figure 13 is specifically a method of operating a reader device (e.g. UE-based reader device or a base station-based reader device) forming part of a wireless communications network and configured to transmit signals to and / or to receive signals from one or more low power devices. The method begins in step Sil. The method comprises, in step S12 receiving an initial access signal from a first low power device among the one or more low power devices, in which the initial access signal requests channel access for communicating on first resources randomly selected by 15 the first low power device according to a contentious access procedure. In step S13, the method comprises associating the first resources to the first low power device. In some embodiments, the method comprises associating both the first resources and second resources to the first low power device, in which the second resources are for performing reader-to-device (R2D) transmission with the first low power device. Next, in step S14, the method comprises transmitting a R2D signal to the first low power device indicating a successful receipt of the initial access signal.. Subsequently, in step SI5, the method comprises performing data transmission with the first low power device based on the first resources. The process ends in step SI6. According to embodiments of the present technique, the R2D signal to the first low power device may be an acknowledge signal or data transmission via the first resources. In some embodiments, the method may comprise reserving the first resources for a successive data transmission. In some embodiments, the method may comprise receiving a successive data transmission from the first low power device on reoccurring resources of the first resources. In some embodiments, the method may comprise associating the first resources to device-to-reader (D2R) data transmission with the first low power device; determining mapping information for mapping the first resources to second resources; and reserving the second resources, based on the mapping information, for performing reader-to-device (R2D) transmission with the first low power device. A sufficient time-gap between D2R and R2D transmissions may be considered to accommodate frequency error caused by SFO / CFO or other circuitry aspects needed to be taken into account. The time-gap may be different depending on the device type and its characteristics. The time-gap may be taken into account when associating R2D resources in relation to D2R resources. In some embodiments, the method may comprise transmitting an initial triggering signal to the one or more low power devices, in which the initial triggering signal comprises time and frequency references. The time and frequency references may indicate a set of time resources and frequency resources; and the time resources may indicate a start and an end of a window allocated to the low power devices or indicate a start of the window and a window length. Additionally, the contentious access procedure may be a slotted ALOHA technique. According to some embodiments of the present technique, the method may comprise associating semi-persistently the first resources allocated to the first low power device, the semi-persistent associating being valid for a predetermined period of time or until another initial access signal is received, and receiving data from the first low power device via the semi-persistently allocated first resources. Additionally, the initial access signal may comprise an identity of the first low power device and / or an identity of the reader device. In some embodiments, where the reader device is an intermediate node, the method may comprise informing a network entity of the resource selection. According to some embodiments of the present technique, the method may comprise transmitting, to the first low power device, a signal to trigger a contention based resource reselection under predetermined conditions, wherein the predetermined conditions includes detecting that no initial access signal is received for a predetermined time indicating congestion for transmitting low power devices. According to some embodiments of the present technique, the method may comprise associating the randomly selected resource for successive transmissions in subsequently reoccurring resources. Furthermore, the randomly selected resources for channel access may be based on TDMA, FDMA, CDMA, or a combination thereof. According to some embodiments of the present technique, the method may comprise monitoring for usage of the randomly selected resources according to the association of first resources. In some embodiments, the association of first resources may be based on energy storage size of the low power device, energy harvesting capability of the low power device, power consumption of the low power device, distance between the low power device and the reader device, or distance between the low power device and a carrier wave emitter. According to some other embodiments of the present technique, the reader device may be a base station or a user equipment (UE). In some embodiments, a UE-based reader device may be an intermediate node, and the resources from the intermediate node to the low power devices may be assigned to the intermediate node by a base station. Figure 14 is a flow diagram illustrating a method of operating a low power device such as an A-loT device configured to transmit signals to and / or to receive signals from reader devices forming part of a wireless communications network in accordance with example embodiments of the present disclosure. The method begins in step S21. The method comprises, in step S22, selecting randomly first resources for performing data transmission with a first reader device among the one or more reader devices. In step S23, the method comprises transmitting an initial access signal to the first reader device, the initial access signal requesting channel access for communicating on the randomly selected first resources according to a contentious access procedure. Next, in step S24, the method comprises receiving a R2D signal from the first reader device indicating a successful receipt of the initial access signal. Subsequently, in step S25, the method comprises performing data transmission with the reader device based on the randomly selected first resources. The process ends in step S26. In some embodiments, the method comprises associating both the first resources and second resources to the first low power device, in which the second resources are for performing reader-to-device (R2D) transmission with the reader device. In some embodiments, the method may comprise receiving an initial triggering signal from the first reader device, in which the initial triggering signal comprises time and frequency references. The time and frequency references may indicate a set of time resources and frequency resources; and the time resources may indicate a start and an end of a window allocated to the low power devices or indicate a start of the window and a window length. Additionally, the contentious access procedure may be a slotted ALOHA technique. According to some embodiments of the present technique, the method may comprise transmitting data to the first reader device via semi-persistently allocated first resources, the semi-persistent allocation being valid for a predetermined period of time or until another initial access signal is transmitted. Furthermore, the initial access signal may comprise an identity of the low power device and / or an identity of the reader device. According to some embodiments of the present technique, the method may comprise receiving, from the first reader device, a signal to trigger a contention based resource reselection under predetermined conditions, wherein the predetermined conditions includes detecting that no initial access signal is received by the first reader device for a predetermined time indicating congestion for transmitting low power devices. In addition, the randomly selected resources for channel access may be based on TDMA, FDMA, CDMA, or a combination thereof. According to some embodiments of the present technique, the method may comprise detecting collision of data transmission on the randomly selected resources according to the association of first resources. In some embodiments, the method may comprise transmitting a low overhead control message to first reader device the upon detection collision of data transmission. In some embodiments, the method may comprise performing a retransmission on the same reoccurring selected resources if the number of detected collisions is below a predetermined threshold. In some embodiments, the method may comprise performing a new channel access request attempt at random resources if the number of detected collisions is above a predetermined threshold. According to some other embodiments of the present technique, the reader device may be a base station or a user equipment (UE). In some embodiments, a UE-based reader device may be an intermediate node, and the resources from the intermediate node to the low power devices may be assigned to the intermediate node by a base station. 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. 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. Therefore, from one perspective there has been described methods, reader devices, communications devices, and circuitry for an energy efficient contention based channel access signaling method for A-IoT devices to access the channel resources. Particular examples of the present disclosure are set out in the following numbered paragraphs: Paragraph 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 low power devices via a radio access interface between the reader device and the one or more low power devices, the method comprising: receiving an initial access signal from a first low power device among the one or more low power devices on first resources randomly selected by the first low power device according to a contentious access procedure; associating the first resources to the first low power device; and transmitting a reader-to-device (R2D) signal to the first low power device indicating a successful receipt of the initial access signal. Paragraph 2. A method according to paragraph 1, wherein the R2D signal to the first low power device is an acknowledge signal or data transmission via the first resources. Paragraph 3. A method according to paragraph 1 or paragraph 2, comprising reserving the first resources for a successive data transmission. Paragraph 4. A method according to any of the preceding paragraphs, comprising receiving a successive data transmission from the first low power device on reoccurring resources of the first resources. Paragraph 5. A method according to any of the preceding paragraphs, comprising associating the first resources to device-to-reader (D2R) data transmission with the first low power device; determining mapping information for mapping the first resources to second resources; and reserving the second resources, based on the mapping information, for performing reader-to-device (R2D) transmission with the first low power device. Paragraph 6. A method according to any of the preceding paragraphs, comprising transmitting an initial triggering signal to the one or more low power devices, the initial triggering signal comprising time and frequency references. Paragraph 7. A method according to paragraph 6, wherein: the time and frequency references indicate a set of time resources and frequency resources; and the time resources indicate a start and an end of a window allocated to the low power devices or indicate a start of the window and a window length. Paragraph 8. A method according to any of the preceding paragraphs, wherein the contentious access procedure is a slotted ALOHA technique. Paragraph 9. A method according to any of the preceding paragraphs, comprising: associating semi-persistently the first resources allocated to the first low power device, the semi-persistent associating being valid for a predetermined period of time or until another initial access signal is received; and receiving data from the first low power device via the semi-persistently allocated first resources. Paragraph 10. A method according to any of the preceding paragraphs, wherein the initial access signal comprises an identity of the first low power device . Paragraph 11. A method according to any of the preceding paragraphs, wherein the initial access signal comprises an identity of the reader device. Paragraph 12. A method according to any of the preceding paragraphs, wherein the reader device is an intermediate node, the method comprising informing a network entity of the resource selection. Paragraph 13. A method according to any of the preceding paragraphs, the method comprising: transmitting, to the first low power device, a signal to trigger a contention based resource reselection under predetermined conditions, wherein the predetermined conditions includes detecting that no initial access signal is received for a predetermined time indicating congestion for transmitting low power devices. Paragraph 14. A method according to any of the preceding paragraphs, comprising: associating the randomly selected resource for successive transmissions in subsequently reoccurring resources. Paragraph 15. A method according to any of the preceding paragraphs, wherein the randomly selected resources for channel access are based on TDMA, FDMA, CDMA, or a combination thereof. Paragraph 16. A method according to any of the preceding paragraphs, comprising: monitoring for usage of the randomly selected resources according to the association of first resources. Paragraph 17. A method according to any of the preceding paragraphs, wherein the association of first resources is based on energy storage size of the low power device, energy harvesting capability of the low power device, power consumption of the low power device, distance 20 between the low power device and the reader device, or distance between the low power device and a carrier wave emitter. Paragraph 18. A method according to any of the preceding paragraphs, wherein the reader device is a base station or a user equipment (UE). Paragraph 19. A method according to any of the preceding paragraphs, wherein the reader device is an intermediate node, the resources from the intermediate node to the low power devices are assigned to the intermediate node by a base station. Paragraph 20. A method according to any of the preceding paragraphs, wherein the low power device is an Ambient loT (A-IoT) device. Paragraph 21. A method according to operating an low power device configured to transmit signals to and / or to receive signals from one or more reader devices forming part of a wireless communications network via a radio access interface between the low power device and the one or more reader devices, the method comprising: transmitting an initial access signal to the first reader device on randomly selected first resources according to a contentious access procedure; and receiving a R2D signal from the first reader device indicating a successful receipt of the initial access signal. Paragraph 22. A method according to paragraph 21, wherein the R2D signal from the first reader device is an acknowledge signal or data transmission via the first resources. Paragraph 23. A method according to paragraph 21 or paragraph 22, comprising reserving the first resources for a successive data transmission. Paragraph 24. A method according to any of paragraphs 21 to 23, comprising performing a successive data transmission with the reader device on reoccurring resources of the first resources. Paragraph 25. A method according to any of paragraphs 21 to 24, comprising receiving reader-to-device (R2D) transmission with the reader devices via second resources, wherein the second resources is determined based on a mapping of the first resources to the second resources. Paragraph 26. A method according to any of paragraphs 21 to 25, comprising receiving an initial triggering signal from the first reader device, the initial triggering signal comprising time and frequency references. Paragraph 27. A method according to paragraph 26, wherein: the time and frequency references indicate a set of time resources and frequency resources; and the time resources indicate a start and an end of a window allocated to the low power devices or indicate a start of the window and a window length. Paragraph 28. A method according to any of paragraphs 21 to 27, wherein the contentious access procedure is a slotted ALOHA technique. Paragraph 29. A method according to any of paragraphs 21 to 28, comprising: transmitting data to the first reader device via semi-persistently allocated first resources, the semi-persistent allocation being valid for a predetermined period of time or until another initial access signal is transmitted. Paragraph 30. A method according to any of paragraphs 21 to 29, wherein the initial access signal comprises an identity of the low power device. Paragraph 31. A method according to any of paragraphs 21 to 30, wherein the initial access signal comprises an identity of the reader device. Paragraph 32. A method according to any of paragraphs 21 to 31, the method comprising: receiving, from the first reader device, a signal to trigger a contention based resource reselection under predetermined conditions, wherein the predetermined conditions includes detecting that no initial access signal is received by the first reader device for a predetermined time indicating congestion for transmitting low power devices. Paragraph 33. A method according to any of paragraphs 21 to 32, wherein the randomly selected resources for channel access are based on TDMA, FDMA, CDMA, or a combination thereof. Paragraph 34. A method according to any of paragraphs 21 to 33, comprising: detecting collision of data transmission on the randomly selected resources according to the association of first resources. Paragraph 35. A method according to any of paragraphs 21 to 34, comprising: transmitting a low overhead control message to first reader device the upon detection collision of data transmission. Paragraph 36. A method according to any of paragraphs 21 to 35, comprising: performing a retransmission on the same reoccurring selected resources if the number of detected collisions is below a predetermined threshold. Paragraph 37. A method according to any of paragraphs 21 to 36, comprising: performing a new channel access request attempt at random resources if the number of detected collisions is above a predetermined threshold. Paragraph 38. A method according to any of paragraphs 21 to 37, wherein the reader device is a base station or a user equipment (UE). Paragraph 39. A method according to any of paragraphs 21 to 38, wherein the reader device is an intermediate node, the resources from the intermediate node to the low power devices are assigned to the intermediate node by a base station. Paragraph 40. A method according to any of paragraphs 21 to 39, wherein the low power device is an Ambient loT (A-IoT) device. Paragraph 41. A communications apparatus operating as a reader device forming part of a wireless communications network, the communications apparatus comprising transceiver circuitry configured to: receive an initial access signal from a first low power device among the one or more low power devices of the wireless communications network via a radio access interface between the one or more low power device and the reader device, on first resources randomly selected by the low power device according to a contentious access procedure; associate the first resources to the first low power device; and transmit a R2D signal to the first low power device indicating a successful receipt of the initial access signal. Paragraph 42. A low power device, comprising transceiver circuitry configured to: transmit an initial access signal to the first reader device of a wireless communications network via a radio access interface between the low power device and the one or more reader devices, on randomly selected first resources according to a contentious access procedure; and receive a R2D signal from the first reader device indicating a successful receipt of the initial access signal. Paragraph 43. Circuity for a communications device operating as a reader device forming part of a wireless communications network, the circuitry comprising transceiver circuitry configured to: receive an initial access signal from a first low power device among the one or more low power devices of the wireless communications network via a radio access interface between the one or more low power device and the reader device, on first resources randomly selected by the low power device according to a contentious access procedure; associate the first resources to the first low power device; and transmit a R2D signal to the first low power device indicating a successful receipt of the initial access signal. Paragraph 44. Circuity for a low power device, the circuitry comprising transceiver circuitry configured to: transmit an initial access signal to the first reader device of a wireless communications network via a radio access interface between the low power device and the one or more reader devices, on randomly selected first resources according to a contentious access procedure; and receive a R2D signal from the first reader device indicating a successful receipt of the initial access signal. Paragraph 45. A computer program which, when the program is executed by a computer, cause the computer to perform the method of paragraph 1 or paragraph 21. Paragraph 46. A non-transitory computer-readable storage medium storing a computer program according to paragraph 45. REFERENCES [1] RP-234058, “New SID: Study on solutions for Ambient loT (Internet of Things) in NR”. RAN plenary #102. Edinburgh. December 2023. [2] TR 38.913, “3rd Generation 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. [3] ‘Study Ambient loT (Internet of Things) in RAN’, 3 GPP TR38.848. https: / / www.3gpp.org / ftp / Specs / archive / 38_series / 38.848 / 38848-i00.zip [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. [5] RP-234065, “New WID: Enhancements of network energy savings for NR,” 3GPP TSG RAN Meeting# 102, Edinburgh, Scotland, December 1 lth-15th, 2023 [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 [7] ‘Study Ambient loT (Internet of Things) in RAN’, 3 GPP TR 38.848. https: / / www.3gpp.org / ftp / Specs / archive / 38_series / 38.848 / 38848-i00.zip [8] Rl-2403821 “Report ofRAN1#116bis meeting”. ETSIMC, 3GPP TSGRAN WG1 #117, Fukuoka, Japan, May 20th - May 24th, 2024. [9] ‘Draft Report of 3GPP TSG RAN WG1 #117 v0.2.0’, 3GPP TSG RAN WG1 #117, Fukuoka, Japan, May 20th - May 24th, 2024.

[10] ‘Study on Low-Power Wake-Up signal and Receiver for NR’, 3GPP TR 38.869. https: / / www.3gpp.org / ftp / Specs / archive / 38 series / 38.869 / 38869-i00.zip

[11] European patent application EP24192725.0

[12] Vazquez-Gallego, Francisco &Alonso, Luis &Alonso-Zarate, Jesus. (2015). Modeling 5 and Analysis of Reservation Frame Slotted-ALOHA in Wireless Machine-to-Machine Area Networks for Data Collection. Sensors (Basel, Switzerland). 15. 3911-31. 10.3390 / sl 50203911.

[13] Rl-2409244 Final FL summary on frame structure and timing aspects for Rel-19 Ambient loT Moderator (vivo)

Claims

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 low power devices via a radio access interface between the reader device and the one or more low power devices, the method comprising:receiving an initial access signal from a first low power device among the one or more low power devices on first resources randomly selected by the first low power device according to a contentious access procedure;associating the first resources to the first low power device; andtransmitting a reader-to-device (R2D) signal to the first low power device indicating a successful receipt of the initial access signal.

2. A method according to claim 1, wherein the R2D signal to the first low power device is an acknowledge signal or data transmission via the first resources.

3. A method according to claim 1 or claim 2, comprising reserving the first resources for a successive data transmission.

4. A method according to any of the preceding claims, comprising receiving a successive data transmission from the first low power device on reoccurring resources of the first resources.

5. A method according to any of the preceding claims, comprisingassociating the first resources to device-to-reader (D2R) data transmission with the first low power device;determining mapping information for mapping the first resources to second resources; andreserving the second resources, based on the mapping information, for performing reader-to-device (R2D) transmission with the first low power device.

6. A method according to any of the preceding claims, comprisingtransmitting an initial triggering signal to the one or more low power devices, the initial triggering signal comprising time and frequency references.

7. A method according to claim 6, wherein:the time and frequency references indicate a set of time resources and frequency resources; andthe time resources indicate a start and an end of a window allocated to the low power devices or indicate a start of the window and a window length.

8. A method according to any of the preceding claims, wherein the contentious access procedure is a slotted ALOHA technique.

9. A method according to any of the preceding claims, comprising:associating semi-persistently the first resources allocated to the first low power device, the semi-persistent associating being valid for a predetermined period of time or until another initial access signal is received; andreceiving data from the first low power device via the semi-persistently allocated first resources.

10. A method according to any of the preceding claims, wherein the initial access signal comprises an identity of the first low power device .

11. A method according to any of the preceding claims, wherein the initial access signal comprises an identity of the reader device.

12. A method according to any of the preceding claims, wherein the reader device is an intermediate node, the method comprising informing a network entity of the resource selection.

13. A method according to any of the preceding claims, the method comprising: transmitting, to the first low power device, a signal to trigger a contention based resource reselection under predetermined conditions, wherein the predetermined conditions includes detecting that no initial access signal is received for a predetermined time indicating congestion for transmitting low power devices.

14. A method according to any of the preceding claims, comprising:associating the randomly selected resource for successive transmissions in subsequently reoccurring resources.

15. A method according to any of the preceding claims, wherein the randomly selected resources for channel access are based on TDMA, FDMA, CDMA, or a combination thereof.

16. A method according to any of the preceding claims, comprising:monitoring for usage of the randomly selected resources according to the association of first resources.

17. A method according to any of the preceding claims, wherein the association of first resources is based on energy storage size of the low power device, energy harvesting capability of the low power device, power consumption of the low power device, distance between the low power device and the reader device, or distance between the low power device and a carrier wave emitter.

18. A method according to any of the preceding claims, wherein the reader device is a base station or a user equipment (UE).

19. A method according to any of the preceding claims, wherein the reader device is an intermediate node, the resources from the intermediate node to the low power devices are assigned to the intermediate node by a base station.

20. A method according to any of the preceding claims, wherein the low power device is an Ambient loT (A-IoT) device.

21. A method according to operating an low power device configured to transmit signals to and / or to receive signals from one or more reader devices forming part of a wireless communications network via a radio access interface between the low power device and the one or more reader devices, the method comprising:transmitting an initial access signal to the first reader device on randomly selected first resources according to a contentious access procedure; andreceiving a R2D signal from the first reader device indicating a successful receipt of the initial access signal..

22. A method according to claim 21, wherein the R2D signal from the first reader device is an acknowledge signal or data transmission via the first resources.

23. A method according to claim 21 or claim 22, comprising reserving the first resources for a successive data transmission.

24. A method according to any of claims 21 to 23, comprising performing a successive data transmission with the reader device on reoccurring resources of the first resources.

25. A method according to any of claims 21 to 24, comprisingreceiving reader-to-device (R2D) transmission with the reader devices via second resources, wherein the second resources is determined based on a mapping of the first resources to the second resources.

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