Communications system, detection station, carrier wave emitter, and methods

Abstract

A controller station, a tag, circuitry and methods for an initial access procedure for multiple tags in a communications system. A controller station broadcasts a control signal for receipt by a plurality of tags. The tags then randomly select a resource element based on information provided in the control signal and emit a signal for receipt by the controller station. The emitted signal may be a backscattered carrier wave signal, or may be a signal generated and transmitted by a tag. Tags may utilise their randomly selected resource element during a multi-tag access procedure.

Description

[0001] COMMUNICATIONS SYSTEM, DETECTION STATION, CARRIER WAVE EMITTER, AND METHODS

[0002] The present application claims the Paris Convention priority of European patent application EP24175293.0, filed 10 May 2024, the contents of which are hereby incorporated by reference.

[0003] BACKGROUND

[0004] Field of the Disclosure

[0005] The present disclosure relates to detection stations of communication systems for detecting backscattered signals by tags which backscatter a carrier wave signal transmitted by a carrier wave emitter. In one example the detection stations may be infrastructure equipment of a wireless communications network. The present disclosure also relates to carrier wave emitters, tags and methods.

[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 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 may not include a power source and may derive power for transmitting signals based on a received radio frequency carrier wave. Such devices may be referred to as “tags”. The disclosed technology relates to improvements in or relating to communication systems which include tags. SUMMARY

[0009] The present disclosure is defined by the claims.

[0010] BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 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:

[0012] Figures 1A and 1 B schematically represent examples of communication systems in which tags are deployed within a coverage area of an infrastructure equipment (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 in accordance with an example embodiment;

[0013] Figure 2 is a schematic block diagram illustrating an example wireless communications network configured in accordance with a 5G or new radio (NR) 3 GPP standard according to example embodiments;

[0014] Figure 3 is a schematic block diagram illustrating in more detail a communications device (UE) and an infrastructure equipment (gNB) formed from components of the wireless communications network shown in Figure 2;

[0015] Figure 4 is a schematic block diagram illustrating an example of backscattering circuitry which may be in employed with example embodiments;

[0016] Figure 5 is a schematic illustration representing an example embodiment in which a carrier wave signal transmitted by an external carrier wave emitter is backscattered according to one example;

[0017] Figure 6 is an example of an A-loT network according to the present disclosure.

[0018] Figure 7 illustrates an example frame structure deployment with a complete IA procedure specified in detail.

[0019] Figure 8 illustrates an example frame structure of the IA procedure.

[0020] Figure 9 illustrates a method including an IA and MA process according to examples of the present disclosure.

[0021] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] Ambient loT

[0023] In release 19 of 3GPP (Rel-19), 3GPP will study Ambient loT [1] where a communications device (UE) is essentially a zero power UE. In Ambient loT, it is considered that the UE can harvest energy to power its communication with the gNB, for example, the energy can be harvested from solar or kinetic energy such as vibrations. Alternatively, the energy to power the device can come from incident RF energy, either directly from a base station (gNB) or from a carrier wave (CW) emitter. An example in which such devices which are powered by radio frequency energy derived from radio signals as a carrier wave transmitted by a carrier wave emitter (CWE) is shown in Figures 1A and 1 B, which consider different example configurations of a communication system according to example embodiments. Figures 1A and 1 B show a plurality of low-power 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 devices 1 are powered as a result of radio frequency energy received from an incident carrier wave (CW) 2 transmitted by the CWE 3. In a first example illustrated by Figure 1 A, a base station 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 signal 2 transmitted by the CWE. In a second example, a detection station in the form of a UE 7 receives a backscattered signal 5 from the tags 1. The detection station or 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, according to example embodiments, a controller station (gNB 4) controls the carrier wave emitters 3 to transmit the carrier waves, and the backscattered signals are detected by detection station (UE) 7 and the detection station reports the detected backscattered signals to the controller station 4. 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.

[0024] 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.

[0025] As shown in Figures 1A and 1 B and in accordance with example embodiments, the gNB 4, which provides a wireless access interface within a cell represented by dashed line 12 controls the CWE 3 to transmit the CW 2 as will be explained below. The gNB 4 therefore has an interface 6 to the CWE 3. In some examples the CWE 3 is formed or controlled by a communications device or UE which operates with a wireless communications network of which the gNB 4 forms part. The gNB 4 can therefore control both a power and an activation of the CW transmitted by the CWE via the interface 6. 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 or reader. In this case, the interface 6 can be an internal interface to the gNB I reader.

[0026] 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).

[0027] In some examples, such as the example of Figure 1 B, the backscattered signal 5 may be received by a separate detection station 7 or reader which does not form part of the gNB 4 and indeed in some examples whilst the CWE 3 are controlled in accordance with example embodiments, this may not form part of a wireless communications network and may be a stand-alone operation. 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. As will be explained below, embodiments of the present technique aim to reduce interference to other devices including those operating with a wireless communications network.

[0028] In some examples the carrier wave emitter 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.

[0029] 5G New Radio (NR) Wireless Communications System

[0030] 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.

[0031] 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.

[0032] 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.

[0033] In terms of broad top-level functionality, the central unit 40 and associated DUs 42 I TRPs 10 may be broadly considered to provide functionality corresponding to the base station 1 of Figure 1. The term network infrastructure equipment I access node may be used to encompass these elements and more conventional base station type elements of wireless telecommunications systems. Depending on the application at hand the responsibility for scheduling transmissions which are scheduled on the radio interface between the respective distributed units and the communications devices may lie with the 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] RF Incident Energy

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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 DFT-s-OFDM waveforms.

[0044] 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 [2], Backscattering Principle

[0045] A passive device can transmit in the 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.

[0046] Different from the conventional wireless 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 IC.

[0047] There are two aspects of power that are relevant to the Ambient loT device:

[0048] • Absorbed power. This is the power that is energy harvested and can be used to drive the circuits within the tag.

[0049] • Reflected power. This is the power that is reflected as a backscattered signal.

[0050] 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 the figure shows the antenna impedance Zaas 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 , 7^ = Z* , rt= 0 holds and thus the received power is completely absorbed by the 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 |Tn| depends on the manufacturing process and may vary within the range of (0,1).

[0051] The absorbed power can be calculated as

[0052] ^in,n=^avail Cl—l ^n ) where Pavai| denotes the power delivered from the antenna when the load impedance perfectly matches with the antenna impedance. Note that in the literature, is defined as the power transmission coefficient [4,5], 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.

[0053] Given PaVau, the average power absorbed by the device can be calculated as

[0054] Where pn,n=i;2denote the ratio of time duration for each impedance state; pt= p2holds if the probability of each impedance equals to the other (this also means same probability of Os and 1 s appeared in the encoded data if the backscattered signal uses a pure OOK waveform). Assuming that there are no antenna losses, the backscattered signal power is calculated as (considering ideal antenna).

[0055] CW Emitter

[0056] Example embodiments address the case that the signal from the tag is backscattered. The carrier-wave emitter (or CW emitter I CWE) 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.

[0057] 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).

[0058] The CW emitter devices may take the following forms:

[0059] • Base station. The base station (e.g. gNodeB) acts as the CW emitter.

[0060] • 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. • 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.

[0061] 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.

[0062] 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.

[0063] 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. Forexample, 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. Based on the downlink command signal, the tag responds with a backscattered signal, where the backscattered signal is backscattered on the carrier wave signal.

[0064] 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.

[0065] 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. 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.

[0066] 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.

[0067] 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.

[0068] 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).

[0069] 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.

[0070] 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 SSB) as the tag’s clock would drift in the meantime.

[0071] According to the present disclosure an efficient access scheme for multiple ambient loT tags is provided.

[0072] The following terminology is used in the following description.

[0073] Slots

[0074] The minimum element in the time domain which is used for segmentation of the transmissions. As the basic element of time resource, slots are deployed in both initial access (IA) and multiple access (MA) phases in the following description. The duration of slots can be different in the initial access and multiple access phases, but in the following description, we assume they are the same for phases.

[0075] Subbands

[0076] The minimum element in the frequency domain. The bandwidth of a subband is assumed to be a multiple of the subcarrier spacing used for the legacy cellular network, e.g., 15 kHzz, 30 kHz, etc. Guard bands may be inserted between two resource elements in order to reduce interference.

[0077] Frequency-time resource elements

[0078] Combining both slots and subbands would yield a two-dimensional resources grid. Each point therein is referred to as a single frequency-time resource element (or ‘resource element’ in short).

[0079] Tag modes

[0080] Energy harvesting mode - tags operating in this mode shall harvest energy from the radio resources.

[0081] Ready mode - tags operating in this mode have been successfully registered with a resource element and wait for the controller station to start the corresponding MA procedure.

[0082] Waiting / holding mode - tags operating in this mode failed to register with a resource element and thus need to wait for the beginning of the next IA procedure.

[0083] Initial Access (IA)

[0084] The access scheme includes an Initial Access (IA) stage. A complete IA procedure / process may incorporate multiple rounds of gNB-broadcasting and tagresponding processes; the objective of introducing a multi-round mechanism is to maximize the resource utilization efficiency of the network when accommodating A-loT devices. For a single round of an IA procedure involving a single CWE, an example IA procedure may include steps selected from the following:

[0085] • Step 1 - gNB schedules one or more of the CWEs that participate in the IA procedure for the CWS transmission.

[0086] • Step 2 - gNB selects a certain tag population, e.g., M tags, and each tag therein is aware that they are selected. Tags can for example be selected based on type (e.g. tag types could be passive vs active or sensor vs asset tracking).

[0087] • Step 3 - gNB broadcasts information to the selected tags; the broadcasting message incorporates 1) number of available resource elements in the current IA round; 2) operating frequency band; 3) number of initially configured rounds for a complete IA establishment. • Step 4 - Based on the received number of resource elements, e.g., N, each tag randomly generates a number nmG [1, TV] with the subscript denoting the tag index. Tags may prepare themselves to receive the CWS for their backscattering transmission (reporting generated number) to the gNB.

[0088] • Step 5 - gNB commands the CWE to transmit CWS to the tags (an example CWS is an unmodulated single-tone, but other CWS structures are also possible). The CWE transmits the CWS under a pre-defined time duration which could span multiples of a single CP-OFDM symbol specified in 3GPP standards.

[0089] • Step 6 - Upon the reception of the CWS, the selected tags shall occupy the resource element which matches with their generated number to backscatter the message; the message may incorporate 1) tag ID and / or 2) a random number generated by the tag.

[0090] • Step 7 - Upon the reception of the received backscattered signal from different tags, gNB shall acknowledge tags with the success of their registration of the resource elements.

[0091] • Step 8 - gNB decides whether to have another round of IA procedure. gNB action o If yes, it repeats steps above. In other words, an IA procedure may include multiple rounds. o If no, it 1) determines whether to reschedule some tags’ resource element for the sake of latency & frequency utilization convenience, e.g., rescheduling certain tags to an earlier transmission slot; and 2) schedules active devices based on the unoccupied resource elements

[0092] It should be noted that the above steps are merely one specific example implementation of an IA procedure, and that various steps may be omitted or modified, and that additional steps may also be included. For example:

[0093] In some cases, those tags whose resource elements have been acknowledged shall remain with ‘ready’ status for the backscattering communication in MA phase.

[0094] Failure of connection - Wheneverthe tag loses the connection with the gNB at any stage, it reconfigures itself to the ‘holding’ mode and waits for the next round of IA procedure if there is any.

[0095] Collision - Whenever there are more than one tags reporting their occupancy on the same resource element, a collision happens. The gNB thus cannot grant acknowledgement to either of the tags. The collided tags shall remain in ‘holding’ mode and wait for next round of IA procedure if there is any. The collided resource element shall be counted as available elements for the next IA round. For an arbitrary CWE, consider that there are N resource elements available in its current IA round. Also, consider that there are N passive devices in the tag population and each of the devices independently picks an integer from the integer set {1, ..., / V] with equal probability. In fact, the integer stands for the index of the resource element. The integer generated by devices along with device ID will be transmitted through the resource element whose index corresponds to the generated integer. Collisions may happen if a single resource element is occupied by more than one device and thus, gNB needs to adaptively schedule the total number of IA rounds to maximize the resource occupancy. Moreover, since the number of available resource elements varies from round to round, gNB may also need to determine whether to extend the IA procedure by allowing extra IA rounds. Given each CWE and the related tag population, gNB may 1) estimate the total number of IA rounds; 2) range of integers from which devices can pick for each IA round.

[0096] Adaptive parameter configuration - gNB shall determine, based on the remaining unoccupied resource elements, 1 ) the range of the random number that tags can generate and 2) the number of remaining rounds to complete IA and 3) the size of the tag population. The determination of round numbers could be based on probabilistic calculation.

[0097] The initial access procedure may operate in multiple rounds. At each round, the reader can determine those tags that have successfully performed initial access. The tags that have not successfully performed initial access can try to perform initial access in a later round. This embodiment allows the gNB I reader to adapt to a varying number of tags in the deployment.

[0098] According to step 7 above, once a tag has successfully performed initial access in a round, it is acknowledged by the reader / gNB. This acknowledgement means that tag does not have to perform initial access in a subsequent round of the initial access procedure. Thus an incremental approach to initial access is provided - once some tags have successfully performed initial access, they do not perform initial access again in a subsequent round and the other unsuccessful tags can occupy the next round.

[0099] During a round of initial access, the gNB can estimate the number of devices that are attempting to perform initial access in the system and can then adapt the amount of resource that is applied to a subsequent initial access round. For example, if it is apparent that a lot of tags have tried to perform initial access in a first round, an increased amount of resource is applied in a second round.

[0100] Furthermore, the gNB can pre-schedule a particular number of rounds in an initial access procedure, e.g. based on the expectation of the number of collided resource elements. Given the number of resource elements and of the tags, the expectation of the collision number takes the following form,

[0101] F[ ] = F[1] + F[2] + - + F[N] (1)

[0102] Where X denotes the number of resource elements being occupied by more than one device. It is the sum of indicator random variables Xit iG [1, / V] where X(= 1 if the resource element i is occupied by more than one device and X(= 0 otherwise.

[0103] The probability that a particular resource element is not occupied by any of the M tags is and the probability that it is occupied by a single tag is M (— )M-1because there are M ways to choose which tag occupies it, a chance for that tag to occupy and — 1 a — chance for each of the other M - 1 tags to not occupy it.

[0104] So the probability P(X = 1) the resource element i is occupied by more than one tag is

[0105] Given that E[X_i] = P(Xt= 1), the expected number of resource elements occupied by more than one tag is

[0106] E[X] = N ■ P( i = 1) (3)

[0107] Based on equation (2) and (3), gNB can estimate the number of collided resource elements, given the number of available resource elements and the tag population in the current IA round. The gNB can then calculate the collision ratio, which is defined by the number of collided resource elements divided by the total number of elements. It may also determine how many rounds would be required for the collision ratio to be reduced to a pre-defined threshold: this is the estimated number of IA rounds. In some cases, the gNB can also determine whether to extend the IA procedure based on the resource element occupancy measured at each round at the cost of increased signalling overhead.

[0108] The rounds of the initial access process are distinguished from the initial access process as a whole. This means that a tag wanting to perform initial access would only do so when a new initial access procedure opportunity is declared, but would not attempt to perform multiple initial accesses during the different rounds of the initial access procedure. This can be facilitated by the initial access procedure containing an ID and the rounds within the initial access procedure containing an ID. The reader would declare that initial access process ‘n’ had started. A tag could take part in multiple rounds of this initial access procedure until it had been successfully acknowledged. However, if a sensor-tag had successfully accessed during an initial round of IA process ‘n’ for sensor reading 1 , it would not be able to send sensor reading 2 during a later round of IA process ‘n’, but would have to wait until IA process ‘n+1 ’. This rule allows the different devices fair access to the system (and prevents some devices from getting excessive access to the system).

[0109] Given that the initial access procedure may comprise multiple rounds, some tags could be given preferential access during earlier rounds than other tags. The reader I gNB could hence indicate the type of tag that has preferential access during each round. For example, a warehouse could have two types of tag: tags that are attached to workers for emergency location of those workers and tags that are attached to parcels. In this case, an initial round of the initial access procedure could be reserved for the tags assigned to workers and other rounds could be reserved for the tags assigned to parcels. This will then allow for some differentiation I prioritization of the tags.

[0110] In some cases, more than one CWE can exist in the A-loT network at different locations. It is beneficial for tags at different location to be energized by the CWS transmitted from a nearby CWE. To achieve this, gNB schedules CWEs in different sessions / rounds throughout time, e.g., there are K C^NEs in total; at session k, only the CWE k takes the charge of CWS emittance. The gNB may control the selection of the tag population for each CWE’s session to make sure that a single tag does not occupy more than one resource element. This could be done by gNB more easily if tags’ location is known by gNB. If the tags’ location is unknown to the gNB, it may randomly select the tag population and command tags that occupy more than one resource element which resource element they should take for each per-CWE IA round. The IA may be marked as completed once the per-CWE IA procedures are finished.

[0111] As an example, Figure 7 illustrates an example frame structure deployment with a complete IA procedure specified in detail. In particular, Figure 7 illustrates a frame structure of the IA procedure for energy-harvesting MA. Considering an example where there are 3 CWEs deployed at different locations in the environment, each of them is scheduled to emit CWS in a sequential order. BA1and BA2denote the frequency bands reserved for the active tags while BBSdenotes the frequency band reserved primarily for the passive tags, albeit active tags can be scheduled to transmit in this band by the gNB. Considering the band BBSwith CWE 2 session as an example, there exist two passivedevice IA rounds followed by an active-device IA round.

[0112] Figure 7 shows the active and passive tags been given different frequency resources. These different frequency resources account for the different characteristics of the devices. The gNB I reader can signal which resources are used for which type of device. Passive tags use frequency resources that are closer to the CWS (compared to active tags). The passive devices preferentially use these resources since:

[0113] Their power consumption is a function of the frequency resource since they need to switch the load impedance at a higher rate to backscatter at a higher frequency.

[0114] The required guard band bandwidth is higherfor passive devices, given theirworse frequency accuracy compared to active devices.

[0115] Passive tags with low energy storage use frequency resources closer to the CWS than passive tags with high energy storage, based on the observation that the power consumption of the tag depends on the switching frequency.

[0116] In general, the switching power consumption is linearly proportional to the switching frequency. Therefore, it can be concluded that the higher the switching frequency, the higher the dynamic power consumption (higher total power consumption).

[0117] As described above, it may therefore be advantageous if certain types of device use certain regions of the frequency resource. Hence, the gNB I reader may indicate (for example in the message that initiates the IA procedure) which resources are used for which types of device. The indication can differentiate devices based on:

[0118] Passive I active type. Passive devices would typically be assigned resources close to the CWS. Stored energy for passive devices. Those passive devices with greater stored energy can use frequency resources that are further from the CWS as they are able to tolerate the higher power drain associated with a higher switching frequency.

[0119] Furthermore, as shown in Figure 7, the tags that require advantageous resources (e.g. passive and energy constrained devices that require resources close to the CWS) may have preferential access to the advantageous resources. Once those tags have had that opportunity, other tags are allowed to attempt to use those resources. The gNB I reader can signal to the tags when resources are reserved for certain tag types and when those resources are freely available. Hence, resources can be reassigned as time progresses.

[0120] For passive devices, the gNB I reader is able to multiplex tags by activating different CWE at different times. For active devices that harvest energy from the CWE, there may be a preferential CWE (from which the tag receives the most powerful CWS) and the tag may wait for that CWE to be active.

[0121] The different CWEs can be activated at different times in order to support time-multiplexing of the tags. Those tags that are close to a CWE will respond at the time that that CWE is active. The different CWEs can also be activated at the same time but with different CWS frequencies in order to support frequency division multiplexing of the tags. Passive tags may respond at the frequency that is transmitted by their local CWE.

[0122] Prior to the tags responding in the initial access procedure, the gNB I reader activates different CWE and the different CWE send out a CWS tone (either at different times or at different frequencies). The tags can then measure the CWS and determine a preferred CWE. The measurement can relate to either (1) the estimated backscattered signal strength from the CWS (this is relevant to passive devices only) or (2) the estimated rate of energy harvesting that is available from the CWS (this is relevant to both the active and passive devices).

[0123] The tags will then determine a preferred CWE that they will use during the initial access phase. Each tag will then wait until the gNB I reader indicates the IA phase that is associated with its preferred CWE and will respond in that IA phase. The tag could determine that multiple CWE are OK (e.g. above a threshold level of CWS reception) and respond in any IA round with one of those multiple CWE. For example, the tag could respond to any of the IA rounds associated with the multiple CWE but stop the IA phase once it has been acknowledged.

[0124] Multiple Access (MA)

[0125] Multiple Access (MA) may be performed after an IA process. That is, MA may be conducted in a per-CWE manner, and may require the corresponding IA completion, no matter which frame structure (short-wait MA & energy-harvesting MA - see below) is deployed.

[0126] The resource elements allocated to tags during the IA procedure are may be used for MA communications in an embodiment. Considering the limited frequency-shifting capability of the passive tags, the frequency resources that have been allocated in IA could be only part of the entire frequency band available for the A-loT network. Since active devices are more capable, they could be assigned with larger frequency shifts. The gNB should be able to allow the repetition of the configured MA for the sake of reliable detection of the backscattered signal, however it may need to inform the tags and CWEs. In the MA procedure, collision should not occur, as the IA process should result in each tag having a particular assigned resource element.

[0127] For a single round of an MA procedure involving a single CWE, an example MA procedure may include steps selected from the following:

[0128] • Step 1 - If needed, gNB broadcasts the start of the MA procedure for a particular CWE, this could be done through message flag / preambles etc.

[0129] • Step 2 - Registered tags that are either in ‘ready’ mode or ‘energy harvesting’ mode should be able to receive the broadcasted command and configure themselves accordingly (tags at ‘ready’ state are already prepared for backscattering and tags in ‘energy harvesting’ mode shall prepare for backscattering).

[0130] • Step 3 - scheduled CWE transmits the CWS to the tags which modulate and scatter back the CWS within their allocated resource element.

[0131] • Step 4 - gNB receives and processes the backscattered signal. Based on the processing result, it determines and broadcasts whether to repeat the same MA procedure or not.

[0132] • Step 5 -According to the frame structure, gNB may schedule 1) the MA for another CWE, or 2) the IA for another CWE.

[0133] • Step 6 - Unless receiving the retransmission command from the gNB, tags that have finished backscattering communication shall switch to holding / energy harvesting status.

[0134] It should be noted that the above steps are merely one specific example implementation of an MA procedure, and that various steps may be omitted or modified, and that additional steps may also be included.

[0135] For a particular CWE, its IA and MA procedure can be executed consecutively, i.e., one IA procedure followed by an MA procedure. Alternatively, the IA procedure for all CWEs are conducted first and followed by the communication in the MA procedure. A drawback of the latter scheme is that the tags that are in ‘ready’ state (i.e., successfully registered with a resource element) need to wait until their transmission session comes and thus may need to consume more power to remain ‘ON’ status. An advantage of having the CWEs’ IA procedures conducted in the first place is that the tag can maintain ‘ready’ state to wait until their scheduled MA session and at the same time, harvest RF energy which is extracted from the other CWEs’ IA procedures. The tag needs to know for how long it can harvest the energy, i.e., according to either some command or built-in timer which does not need to be strictly accurate. This results in the following 2 frame structures:

[0136] Structure 1 (short-wait MA): CWE1 IA -> CWE1 MA -> CWE2 IA -> CWE2 MA ...

[0137] Structure 2 (long-wait I energy-harvesting MA): CWE1 IA -> CWE2 IA -> CWE1 MA -> CWE2 MA ...

[0138] In particular, a short wait MA round directly follows an IA round, and a long wait MA round follows multiple IA rounds. For both structure types, the gNB may need to broadcast an lA-stopped / MA-started signaling. The short wait and long wait procedures don’t necessarily need to be associated with CWEs and can just be associated with readers, where multiple IA rounds could be used for example in order to resolve collisions. Hence, short wait MA could simply be associated with an alternating sequence of IA rounds and MA rounds whereas a long wait MA could be associated with multiple IA rounds followed by multiple MA rounds.

[0139] Figure 8 illustrates an example frame structure of an IA procedure for Structure 1 (shortwait MA)..For each CWE, the IA and MA are conducted consecutively, which are followed by the same procedures for other CWEs. Note that the IA and MA procedures may follow the same steps as described above. The difference only arises from the execution order of IA and MA procedures.

[0140] After a tag has successfully performed an IA round (i.e. it has received an acknowledgement), it will consume energy before it takes part in the MA round. This is because the tag needs some power to maintain its state between the IA round and MA round (e.g. the tag needs to remember its allocated resources between the IA round and MA round and keeping the memory alive consumes power). Hence, the gNB I reader needs to decide whether to perform short wait or long wait MA procedures.

[0141] Note that a short wait procedure is preferable for tags that have a limited amount of stored energy whereas a long wait procedure is preferable from the spectral efficiency perspective (since the gNB I reader can understand which resources are required for a larger number of tags and allocate resources for those multiple tags in a more resource efficient way).

[0142] The reader I gNB can apply either short wait or long wait MA procedures. Some procedures can be short wait and some can be long wait. In an embodiment, the gNB I reader signals whether a short wait or long wait MA procedure is being applied and the tag chooses to respond eitherto the short wait orto the long wait MA procedure depending on the status of the tag (e.g. depending on the energy stored in the tag).

[0143] Furthermore, as described, there may be multiple IA and MA rounds during the procedure. During the whole procedure, tags will be harvesting energy from the CWS. Referring to step 2 above, a tag does not need to take part in every IA round or MA round. It can wait until it has harvested sufficient energy and then participate in the subsequent IA I MA round. The gNB I reader can determine whether a signal has been received by a device during an MA round (e.g. by determining whether the received backscattered signal has a level that is above a threshold). It can then ignore the tag’s receptions when the backscattered signal strength is below the threshold. Based on repeated observations of when the tag is able to participate in MA rounds (i.e. when the tag has sufficient energy to participate in an MA round), the reader I gNB can predict when the tag will not be transmitting in an MA round (e.g. assuming that the tag has not harvested sufficient energy based on an energy harvesting rate) and reassign those MA rounds to other tags. This will increase the spectral efficiency of the system.

[0144] Figure 9 shows an example method according to the present disclosure. The controller station 110 of a communication system executes a first initial access process 210 for a plurality of tags 130 (i.e. ambient communications devices configured to backscatter carrier wave signals for receipt by the controller station). The controller station 110 has a control interface with one or more CWEs 120. The controller station may be an infrastructure equipment forming part of a radio network of a wireless communications network (e.g. a gNB). In some examples, the controller station is an infrastructure equipment of a radio network part of a wireless communications network and the transmitter circuitry is configured to transmit signals to communications devices via a wireless access interface provided by a wireless communications network and the receiver circuitry is configured to receive signals from the communications devices transmitted via the wireless access interface, and the interface with the controller station is formed by the wireless access interface, and the detection station is a wireless communications device which detects the backscattered signals and the controller station receives an indication of the backscattered signals received from the communications device transmitted via the wireless access interface. Furthermore, the interface with the one or more carrier wave emitters may be formed by a wireless access interface provided by an infrastructure equipment and a communications device which includes transceiver circuitry configured to transmit and to receive radio signals via the wireless access interface provided by the wireless communications network, the communications device forming part of the one or more carrier wave emitters, the interface of the controller station formed by the infrastructure equipment uses the wireless access interface of the wireless communications network. In some cases, the one or more carrier wave emitters may form part of the controller station.

[0145] The first initial access process 210 includes broadcasting, by the controller station 110, a first control signal 901 for receipt by the plurality of tags, wherein the first control signal indicates resource information for the first initial access process for the plurality of tags. The first control signal may indicate that only a particular subset of the plurality of tags are to participate in the first initial access process. For example, the particular subset of the plurality of tags comprises devices of a particular type, devices having particular identifiers, and / or may be based on a priority level of the plurality of tags. The first control signal 901 may in some cases indicate a number of pre-scheduled initial access processes, the first control signal may also indicate that tags which successfully register in first initial access process should not attempt to register in remaining pre-scheduled initial access processes, however this behaviour may additionally or alternatively be preconfigured for the tags. In addition, the number of prescheduled initial access processes may be based on an estimated number of the plurality of tags. The resource information indicated in the first control signal 901 may indicate a set of resource elements to be used for backscattered signals from the plurality of tags, e.g. by indicating a number of resource elements and a frequency band. In some cases the number of resource elements may be based on an estimate number of the plurality of tags. Moreover, the resource information may comprise first resource information for a first subset of the plurality of tags, and second resource information for a second subset of the plurality of tags, wherein the first resource information is different to the second resource information, and wherein devices of the first subset of the plurality of tags do not belong to the second subset of the plurality of tags. The first and second subsets of the plurality of tags may comprise devices of different types, e.g. the first subset comprises passive devices without a battery for energy storage, and wherein the second subset comprises semi-passive devices having a battery for energy storage. As such, the first subset of the plurality of tags may be assigned a first set of resource elements, and the second subset of the plurality of tags may be assigned a second set of resource elements, wherein the first set of resource elements may have a smaller absolute frequency than the second set of resource elements.

[0146] Returning to Figure 9, the method includes transmitting, by the controller station 110, a first instruction 902 to one or more carrier wave emitters (CWEs) to transmit a first carrier wave signal (CWS) 903 for receipt by the plurality of tags for the first initial access process 210. Although not shown in Figure 9, the controller station may have a control interface with a plurality of CWEs of the communications system. Accordingly the first instruction transmitted to the one or more CWEs instructs one or more particular CWEs of the plurality of CWEs based on an estimated geographical distribution of the plurality of tags. Moreover, the first instruction may instruct particular CWEs of the plurality of CWEs to transmit respective first CWSs at different times, and / or at different frequencies. The first instruction may instruct the one or more CWEs to transmit the first CWS for a pre-defined time duration. Furthermore, in some examples the first CWS is an unmodulated single-tone CWS, however other tones are contemplated.

[0147] In some cases, the method may also comprise transmitting a preliminary control signal to the plurality of CWEs, wherein the preliminary control signal instructs the plurality of CWEs to transmit, at different times, respective reference CWSs for receipt by the plurality of tags, wherein the reference CWSs are for the plurality of tags to select one or more respective preferred CWE of the plurality of CWEs based on the reference CWSs, and wherein a backscattered signal may be received from a particular tag in response to a first CWS signal 903 transmitted by a preferred CWE for the particular tag.

[0148] In the following description, the signals sent from tags are described as backscattered signals. It will be appreciated by a skilled artisan that a passive tag may reflect a CWS as a backscattered signal and an active tag may actively generate a transmit signal. For the sake of brevity, the description refers to backscattered signals and the skilled artisan will appreciate that an active tag would actively transmit a signal referred to as a backscattered signal. The method additionally includes the step of transmitting, by the CWE 120 and in response to the first instruction 902, a CWS 903 for use by the tags 130 to backscatter signals or harvest energy. The tags 130 (e.g. a passive tag) may reflect / backscatter the CWS 903 (i.e. transmit backscattered signals 904) for receipt by the controller station 110. The tags 130 may reflect / backscatter the CWS 903 (i.e. transmit the backscattered signals 904) on a randomly selected resource element (of the resource elements indicated in the control signal 901). An active tag may generate a signal (e.g. in response to the first control signal 901) and transmit it on a randomly selected resource element (of the resource elements indicated in the control region 901). As such, the backscattered (or transmitted) signals 904 from the first set of tags are received by the controller station 110 on randomised resource elements according to the resource information for the first initial access process 210. In other words, emitted signals 904 are received by the controller station, where the emitted signals 904 may include backscattered signals from passive devices and / or transmitted signals from active devices.

[0149] The backscattered signals 904 may each indicate the random number used to select the resource element used for the backscattered signal 904, and may also indicate a tag identifier of a tag 130 which performed the backscattering for the respective backscattered signal 904. In some cases, the backscattered signals 904 may be received by a detector station (not shown) and forwarded to the controller station 110.

[0150] Returning to Figure 9, the method includes step 905 of broadcasting, by the controller station 110, a second control signal 905 for receipt by the first set of tags (i.e. successfully registered tags), wherein the second control signal indicates successful registration of the tags in the first initial access process 210 (i.e. acknowledges the backscattered signal 904). In some cases, backscattered signals 904 from two or more tags 130 may be received on a particular resource element thereby causing a collision. In such cases, these tags are not registered and the second control signal 905 does not indicate successful registration of these tags. Furthermore, the second control signal 905 may instruct these tags with collided backscattered signals 905 to enter a waiting state in which the tags are to wait for a subsequent initial access process to attempt registration. The resource on which the collision occurred may be made available for any such subsequent initial access process.

[0151] The controller station 110 may store an association between a resource element on which a particular backscattered signal is received with a particular tag from which the particular backscattered signal is received. As such, the controller station 110 may associate future transmissions in a multiple access process 220 on a particular resource element with a particular tag 130.

[0152] In some cases, the second control signal 905 may indicate a state for the one or more tags to enter. For example, the second control signal 905 may instruct a tag to enter a ready state, an energy harvesting state, and a waiting state. The state for the one or more tags to enter may be based on a number of backscattered signals received by the controller station, and / or a number of tags successfully registered in the first initial access process, and / or a particular device type of the one or more tags. After completing the first initial access process, the controller station 110 may determine whether to execute a further initial access process (not shown). In other words, the controller station 110 selectively executes a second initial access process. The selective execution of the second initial access process may be based on a number of prescheduled initial access processes, and / or a number of tags successfully registered in the first initial access process 210, and / or an estimated total number of tags.

[0153] In some cases, the resource information for the second initial access process may be different to the resource information for the first initial access process 210. For example, resource information for the second initial access process may indicate a different number of resource elements to the resource information for the first initial access process. This may be done to provide a greater number of resource elements in the second initial access process if, for example, the number of tags registered in the first initial access process 210 is above a predetermined threshold, or e.g. if a predicted number of collisions in the first initial access process 210 is above a predetermined threshold. Furthermore, resource elements associated with tags which successfully registered in the first initial access process 210 may not be indicated as available for the second initial access process. However, resource elements on which two or more backscattered signals 904 collided during the first initial access process 210 may be indicated as available for the second initial access process.

[0154] In addition, multiple initial access processes may be considered to be rounds of an overall access procedure. In other words, the first initial access process and the second initial access process may be considered to be part of a first group of initial access operations. Therefore, an identifier for the first group of initial access processes (i.e. overall access procedure) may be indicated in one or more control signals, of each of the first and second initial access processes. In this manner, tags which have successfully registered during the first initial access procedure can be prevented from attempting to register during the second initial access procedure, and said tags can be permitted to register during a subsequent overall access procedure (i.e. during a second group of initial access operations).

[0155] Returning to Figure 9, the controller station 110 may execute a multi-tag access process (i.e. multiple access (MA) process) 220. The MA process may include transmitting, by the controller station 110, a second instruction 906 to one or more CWEs 120 to transmit a second CWS for receipt by registered tags of the plurality of tags. In response to receiving the second instruction 906, the CWE 120 may transmit a CWS 907 for receipt by the registered tags 130. The tags 130 may reflect / backscatter the CWS 907 (i.e. transmit a backscattered signal 908) for receipt by the controller station 110.

[0156] Multiple MA processes may be executed for different CWEs, as discussed above. For example, a second MA process (not shown) may be executed for registered tags from which backscattered signals are not received in the first MA process 220. Additional MA processes may be executed based on a number of registered tags from which backscattered signals are not received in the first multi-tag access process. As discussed above, multiple IA and multiple MA processes may be scheduled. This may be done, e.g. sequentially according to an energy storage capability of respective subsets of tags. For example, according to Structure 2 (the long wait MA structure) above, the controller station 110 may proceed by executing the first initial access process 210 at a first time, executing a second initial access process at a second time, executing the first multi-tag access process 220 at a third time, and executing a second multi-tag access process at a fourth time, wherein the second time is after the first time, the third time is after the second time, and the fourth time is after the third time. Alternatively, according to Structure 1 above the controller station 110 may proceed by executing the first initial access process at a first time, executing the first multi-tag access process at a second time, executing a second initial access process at a third time, and executing a second multi-tag access process at a fourth time, wherein the second time is after the first time, the third time is after the second time, and the fourth time is after the third time

[0157] Therefore, from one perspective there has been described a controller station, a tag, circuitry and methods for an initial access procedure for multiple tags in a communications system. A controller station broadcasts a control signal for receipt by a plurality of tags. The tags then randomly select a resource element based on information provided in the control signal and emit a signal for receipt by the controller station. The emitted signal may be a backscattered carrier wave signal, or may be a signal generated and transmitted by a tag. Tags may utilise their randomly selected resource element during a multi-tag access procedure.

[0158] Further embodiments are set out in the following numbered clauses:

[0159] 1. A controller station of a communications system, the controller station having a control interface with one or more carrier wave emitters of the communications system for controlling the one or more carrier wave emitters to transmit carrier wave signals for receipt by one or more tags, wherein the tags are ambient communications devices configured to backscatter carrier wave signals for receipt by the controller station, wherein the controller station comprises: transmitter circuitry for transmitting signals, receiver circuitry for receiving signals, and controller circuitry configured with the transmitter circuitry and receiver circuitry to: execute a first initial access process for a plurality of tags, wherein executing the first initial access process comprises: broadcasting a first control signal for receipt by the plurality of tags, wherein the first control signal indicates resource information for the first initial access process for the plurality of tags; transmitting a first instruction to one or more carrier wave emitters (CWEs) to transmit a first carrier wave signal (CWS) for backscattering by the plurality of tags for the first initial access process; receiving, according to the resource information, backscattered CWS signals from a first set of tags of the plurality of tags; and broadcasting a second control signal for receipt by the first set of tags, wherein the second control signal indicates successful registration of the first set of tags in the first initial access process.

[0160] 2. The controller station according to clause 1 , wherein the controller station is an infrastructure equipment forming part of a radio network of a wireless communications network.

[0161] 3. The controller station according to clause 1 or clause 2, wherein the controller station is an infrastructure equipment of a radio network part of a wireless communications network and the transmitter circuitry is configured to transmit signals to communications devices via a wireless access interface provided by a wireless communications network and the receiver circuitry is configured to receive signals from the communications devices transmitted via the wireless access interface, and the interface with the controller station is formed by the wireless access interface, and the detection station is a wireless communications device which detects the backscattered signals and the controller station receives an indication of the backscattered signals received from the communications device transmitted via the wireless access interface.

[0162] 4. The controller station according to any preceding clause, wherein the interface with the one or more carrier wave emitters is formed by a wireless access interface provided by an infrastructure equipment and a communications device which includes transceiver circuitry configured to transmit and to receive radio signals via the wireless access interface provided by the wireless communications network, the communications device forming part of the one or more carrier wave emitters and the interface of the controller station formed by the infrastructure equipment uses the wireless access interface of the wireless communications network.

[0163] 5. The controller station according to any preceding clause, wherein the one or more carrier wave emitters form part of the controller station.

[0164] 6. The controller station according to any preceding clause, wherein the first control signal indicates that only a particular subset of the plurality of tags are to participate in the first initial access process. 7. The controller station according to clause 6, wherein the particular subset of the plurality of tags comprises devices of a particular type.

[0165] 8. The controller station according to clause 6 or clause 7, wherein the particular subset of the plurality of tags comprises devices having particular identifiers.

[0166] 9. The controller station according to any of clauses 6-8, wherein the particular subset of the plurality of tags is based on a priority level of the plurality of tags.

[0167] 10. The controller station according to any preceding clause, wherein the first control signal indicates a number of pre-scheduled initial access processes.

[0168] 11. The controller station according to clause 10, wherein the first control signal indicates that tags which successfully register in a first initial access process should not attempt to register in remaining pre-scheduled initial access processes.

[0169] 12. The controller station according to clause 10 or 11 , wherein the number of prescheduled initial access processes is based on an estimated number of the plurality of tags.

[0170] 13. The controller station according to any preceding clause, wherein the resource information is based on an estimated number of the plurality of tags.

[0171] 14. The controller station according to any preceding clause, wherein the resource information indicates a set of resource elements to be used for the backscattered CWS signals from the plurality of tags.

[0172] 15. The controller station according to clause 14, wherein the set of resource elements is indicated as a number of resource elements and a frequency band.

[0173] 16. The controller station according to any preceding clause, wherein the resource information comprises first resource information for a first subset of the plurality of tags, and second resource information for a second subset of the plurality of tags, wherein the first resource information is different to the second resource information, and wherein devices of the first subset of the plurality of tags do not belong to the second subset of the plurality of tags.

[0174] 17. The controller station according to clause 16, wherein first and second subsets of the plurality of tags comprise devices of different types.

[0175] 18. The controller station according to clause 17, wherein the first subset comprises passive devices without a device for energy storage, and wherein the second subset comprises semi-passive devices having a device for energy storage.

[0176] 19. The controller station according to clause 17, wherein the first subset comprises passive devices that backscatter a CWS, and wherein the second subset comprises active devices that actively generate a signal for transmission.

[0177] 20. The controller station according to clause 18 or 19, wherein the first subset of the plurality of tags are assigned a first set of resource elements, and the second subset of the plurality of tags are assigned a second set of resource elements, wherein the first set of resource elements have a smaller absolute frequency than the second set of resource elements.

[0178] 21. The controller station according to any preceding clause, wherein the controller station has a control interface with a plurality of CWEs of the communications system.

[0179] 22. The controller station according to clause 21 , wherein the first instruction transmitted to the one or more CWEs instructs one or more particular CWEs of the plurality of CWEs based on an estimated geographical distribution of the plurality of tags.

[0180] 23. The controller station according to clause 21 or clause 22, wherein the first instruction instructs particular CWEs of the plurality of CWEs to transmit respective first CWSs at different times.

[0181] 24. The controller station according to any of clauses 21-23, wherein the first instruction instructs particular CWEs of the plurality of CWEs to transmit respective first CWSs at different frequencies. 25. The controller station according to any of clauses 21-24, further comprising: transmitting a preliminary control signal to the plurality of CWEs, wherein the preliminary control signal instructs the plurality of CWEs to transmit, at different times, respective reference CWSs for receipt by the plurality of tags, and wherein a backscattered signal is received from a particular tag in response to a first CWS signal transmitted by a preferred CWE for the particular tag.

[0182] 26. The controller station according to any preceding clause, wherein the first instruction instructs the one or more CWEs to transmit the first CWS for a pre-defined time duration.

[0183] 27. The controller station according to any preceding clause, wherein the first CWS is an unmodulated single-tone CWS.

[0184] 28. The controller station according to any preceding clause, wherein the backscattered signals from the first set of tags are received on randomised resource elements according to the resource information for the first initial access process.

[0185] 29. The controller station according to clause 28, wherein the backscattered signals each indicate a random number used to select the resource element on which the backscattered signal was transmitted.

[0186] 30. The controller station according to any preceding clause, wherein the backscattered signals indicate a tag identifier of a tag of the first set of tags from which the respective backscattered signal is received.

[0187] 31 . The controller station according to any preceding clause, wherein one or more of the backscattered signals are received via a detector station of the communications system.

[0188] 32. The controller station according to any preceding clause, wherein two or more backscattered signals are received on a particular resource element from two or more respective tags of the plurality of tags, and wherein the second control signal does not indicate successful registration of the two or more tags. 33. The controller station according to clause 32, wherein the second control signal instructs tags which transmitted backscattered signals on the particular resource element to enter a waiting state, in which the tags are to wait for a subsequent initial access process to attempt registration.

[0189] 34. The controller station according to any preceding clause, further comprising storing an association between a resource element on which a particular backscattered signal is received with a particular tag from which the particular backscattered signal is received.

[0190] 35. The controller station according to any preceding clause, wherein the second control signal indicates a state for the one or more tags to enter.

[0191] 36. The controller station according to clause 35, wherein the state for the one or more tags to enter is based on a number of backscattered signals received by the controller station.

[0192] 37. The controller station according to clause 35 or 36, wherein the state for the one or more tags to enter is based on a number of tags successfully registered in the first initial access process.

[0193] 38. The controller station according to any of clauses 35-37, wherein the state for the one or more tags to enter indicated in the second control signal is based on a particular device type of the one or more tags.

[0194] 39. The controller station according to any of clauses 35-38, wherein the state for the one or more tags to enter is one or more of: a ready state, an energy harvesting state, and a waiting state.

[0195] 40. The controller station according to any preceding clause, further comprising selectively executing a second initial access process for a CWE of the communications system.

[0196] 41. The controller station according to clause 40, wherein the selective execution of the second initial access process is based on number of pre-scheduled initial access processes. 42. The controller station according to clause 40 or 41 , wherein the selective execution of the second initial access process is based on a number of tags in a first set of tags.

[0197] 43. The controller station according to any of clauses 40-42, wherein resource information for the second initial access process is different to the resource information for the first initial access process.

[0198] 44. The controller station according to clause 43, wherein resource information for the second initial access process indicates a different number of resource elements to the resource information for the first initial access process.

[0199] 45. The controller station according to clause 44, wherein, based on a number of tags in the first set of tags being above a predetermined threshold, the resource information for the second initial access process indicates a greater number of resource elements than the resource information for the first initial access process.

[0200] 46. The controller station according to any of clauses 43-45, wherein the resource information for the second initial access process does not include resource elements associated with tags which successfully registered in the first initial access process.

[0201] 47. The controller station according to any of clauses 40-46, wherein the resource information for the second initial access process indicates a set of resource elements including a particular resource element on which two or more backscattered signals were received from two or more respective tags of the plurality of tags during the first initial access process.

[0202] 48. The controller station according to any of clauses 40-47, wherein the first initial access process and the second initial access process are part of a first group of initial access operations, wherein an identifier for the first group of initial access processes is indicated in one or more control signals of each of the first and second initial access processes; wherein the controller station is further configured to execute a third initial access process, wherein the third initial access process is part of a second group of initial access operations, and wherein an identifier for the second group of initial access processes is indicated in one or more control signals of the third initial access processes. 49. The controller station according to clause 48, wherein the controller station is configured to prevent tags which have successfully registered during the first initial access procedure from attempting to register during the second initial access procedure, and permit tags which have successfully registered during the first initial access procedure to register during the third initial access procedure.

[0203] 50. The controller station according to any preceding clause, further comprising: executing a first multi-tag access process comprising: transmitting a second instruction to one or more CWEs to transmit a second CWS for receipt by registered tags of the plurality of tags; and receiving backscattered signals from one or more of the registered tags on resource elements on which the respective backscattered signals in the first initial access process were received.

[0204] 51 . The controller station according to clause 50, further comprising: selectively executing a second multi-tag access process for a subset of the registered tags from which backscattered signals are not received in the first multi-tag access process, wherein the second multi-tag access process is executed using CWEs which were not utilised in the first multi-tag access process.

[0205] 52. The controller station according to clause 51 , wherein the second multi-tag access process is selectively executed based on a number of registered tags from which backscattered signals are not received in the first multi-tag access process.

[0206] 53. The controller station according to clause 51 or 52, comprising executing a plurality of initial access processes and a plurality of multi-tag access processes.

[0207] 54. The controller station according to clause 53, wherein the plurality of initial access processes and a plurality of multi-tag access processes are sequentially scheduled according to an energy storage capability of respective subsets of tags.

[0208] 55. The controller station according to clause 53 or 54, comprising: executing the first initial access process at a first time, executing a second initial access process at a second time, executing the first multi-tag access process at a third time, and executing a second multi-tag access process at a fourth time, wherein the second time is after the first time, the third time is after the second time, and the fourth time is after the third time.

[0209] 56. The controller station according to clause 53 or 54, comprising: executing the first initial access process at a first time, executing the first multi-tag access process at a second time, executing a second initial access process at a third time, and executing a second multi-tag access process at a fourth time, wherein the second time is after the first time, the third time is after the second time, and the fourth time is after the third time.

[0210] 57. A communications system comprising: the controller station according to any of clauses 1-56; and the one or more CWEs, wherein the one or more CWEs are configured to, in response to receiving the first instruction, transmit a CWS for backscattering by the plurality of tags.

[0211] 58. The communications system of clause 56, further comprising: one or more detector stations configured to receive backscattered signals from the plurality of tags and forward the received backscattered signals to the controller station.

[0212] 59. Circuitry for a controller station of a communications system, the controller station having a control interface with one or more carrier wave emitters of the communications system for controlling the one or more carrier wave emitters to transmit carrier wave signals for receipt by one or more tags, wherein the tags are ambient communications devices configured to backscatter carrier wave signals for receipt by the controller station, wherein the controller station comprises: transmitter circuitry for transmitting signals, receiver circuitry for receiving signals, and controller circuitry configured with the transmitter circuitry and receiver circuitry to: execute a first initial access process for a plurality of tags, wherein executing the first initial access process comprises: broadcasting a first control signal for receipt by the plurality of tags, wherein the first control signal indicates resource information for the first initial access process for the plurality of tags; transmitting a first instruction to one or more carrier wave emitters (CWEs) to transmit a first carrier wave signal (CWS) for backscattering by the plurality of tags for the first initial access process; receiving, according to the resource information, backscattered CWS signals from a first set of tags of the plurality of tags; and broadcasting a second control signal for receipt by the first set of tags, wherein the second control signal indicates successful registration of the first set of tags in the first initial access process.

[0213] 60. A method for a controller station of a communications system, the controller station having a control interface with one or more carrier wave emitters of the communications system for controlling the one or more carrier wave emitters to transmit carrier wave signals for receipt by one or more tags, wherein the tags are ambient communications devices configured to backscatter carrier wave signals for receipt by the controller station, the method comprising: executing a first initial access process for a plurality of tags, wherein executing the first initial access process comprises: broadcasting a first control signal for receipt by the plurality of tags, wherein the first control signal indicates resource information for the first initial access process for the plurality of tags; transmitting a first instruction to one or more carrier wave emitters (CWEs) to transmit a first carrier wave signal (CWS) for backscattering by the plurality of tags for the first initial access process; receiving, according to the resource information, backscattered CWS signals from a first set of tags of the plurality of tags; and broadcasting a second control signal for receipt by the first set of tags, wherein the second control signal indicates successful registration of the first set of tags in the first initial access process.

[0214] 61. A tag configured to backscatter carrier wave signals for receipt by a controller station of a communications system, the tag being an ambient communications device, wherein the tag comprises: energy harvesting circuitry configured to harvest energy from incident carrier wave signals, backscattering circuitry configured to receive incident carrier wave signals and transmit backscattered signals for receipt by the controller station, and controller circuitry configured with the backscattering circuitry to: receive a first control signal from the controller station, wherein the first control signal indicates resource information for a first initial access process for the tag to register with the controller station; backscatter, based on the resource information, an incident carrier wave signal (CWS) from a carrier wave emitter (CWE) for receipt by the controller station using a randomly selected resource element.

[0215] 62. The tag according to clause 61 , wherein the first control signal indicates that only tags meeting one or more criteria are to participate in the first initial access procedure, and wherein the tag is configured to determine, based on the first control signal, that the tag meets the one or more criteria.

[0216] 63. The tag according to clause 62, wherein the one or more criteria comprise the tag being a particular type of device.

[0217] 64. The tag according to clause 62 or 63, wherein the one or more criteria comprise the tag having a particular identifier.

[0218] 65. The tag according to any of clauses 62-64, wherein the one or more criteria comprise a priority level of the tag.

[0219] 66. The tag according to any of clauses 61-65, wherein the tag is an active device further comprising: energy storage means configured to receive energy from the energy harvesting circuitry, and configured to supply energy to the backscattering and controller circuitry.

[0220] 67. The tag according to any of clauses 61-65, wherein the tag is a passive device, wherein the energy harvesting circuitry is configured to supply energy to the backscattering and controller circuitry.

[0221] 68. The tag according to any of clauses 61-67, wherein the tag is configured to randomly select a resource element based on generating a random number.

[0222] 69. The tag according to any of clauses 61-68, wherein the backscattered CWS includes an identifier for the tag. 70. The tag according to any of clauses 61-69, wherein the tag is further configured to: receive a second control signal from the controller station, wherein the second control signal indicates successful registration of the tag in the first initial access process.

[0223] 71. The tag according to clause 70, wherein the tag is further configured to: determine, based on the second control signal, not to attempt registration in a second initial access procedure.

[0224] 72. The tag according to clause 71 , wherein the first and second initial access procedures are part of a first group of initial access operations, wherein an identifier for the first group of initial access processes is indicated in one or more control signals of each of the first and second initial access processes.

[0225] 73. The tag according to clause 72, wherein the tag is further configured to attempt registration in a third initial access procedure, wherein the third initial access process is part of a second group of initial access operations, and wherein an identifier for the second group of initial access processes is indicated in one or more control signals of the third initial access processes.

[0226] 74. The tag according to any of clauses 70-73, wherein the tag is further configured to: backscatter a further CWS from a CWE, for receipt by the controller station, wherein the backscattered further CWS utilises the randomly selected resource element.

[0227] 75. Circuitry for a tag configured to backscatter carrier wave signals for receipt by a controller station of a communications system, the tag being an ambient communications device, wherein the circuitry comprises: energy harvesting circuitry configured to harvest energy from incident carrier wave signals, backscattering circuitry configured to receive incident carrier wave signals and transmit backscattered signals for receipt by the controller station, and controller circuitry configured with the backscattering circuitry to: receive a first control signal from the controller station, wherein the first control signal indicates resource information for a first initial access process for the tag to register with the controller station; backscatter, based on the resource information, an incident carrier wave signal (CWS) from a carrier wave emitter (CWE) for receipt by the controller station using a randomly selected resource element.

[0228] 76. A method for a tag configured to backscatter carrier wave signals for receipt by a controller station of a communications system, the tag being an ambient communications device, wherein the method comprises: receiving a first control signal from a controller station of a communications system, wherein the first control signal indicates resource information for a first initial access process for the tag to register with the controller station; backscatter, based on the resource information, an incident carrier wave signal (CWS) from a carrier wave emitter (CWE) for receipt by the controller station using a randomly selected resource element.

[0229] 77. A tag configured to transmit signals for receipt by a controller station of a communications system, the tag being an ambient communications device, wherein the tag comprises: transceiver circuitry configured to receive incident carrier wave signals and transmit signals for receipt by the controller station, and controller circuitry configured with the backscattering circuitry to: receive a first control signal from the controller station, wherein the first control signal indicates resource information for a first initial access process for the tag to register with the controller station; transmit, based on the resource information, a signal for receipt by the controller station using a randomly selected resource element.

[0230] 78. A controller station of a communications system, the controller station having a control interface with one or more carrier wave emitters of the communications system for controlling the one or more carrier wave emitters to transmit carrier wave signals for receipt by one or more tags, wherein the tags are ambient communications devices, wherein the controller station comprises: transmitter circuitry for transmitting signals, receiver circuitry for receiving signals, and controller circuitry configured with the transmitter circuitry and receiver circuitry to: execute a first initial access process for a plurality of tags, wherein executing the first initial access process comprises: broadcasting a first control signal for receipt by the plurality of tags, wherein the first control signal indicates resource information for the first initial access process for the plurality of tags; receiving, according to the resource information, signals emitted from a first set of tags of the plurality of tags; and broadcasting a second control signal for receipt by the first set of tags, wherein the second control signal indicates successful registration of the first set of tags in the first initial access process.

[0231] Numerous modifications and variations of the present disclosure are possible in light of the above teachings. It is therefore to be understood that, within the scope of the clauses, the disclosure may be practiced otherwise than as specifically described herein.

[0232] In so far as embodiments of the disclosure have been described as being implemented, at least in part, by one or more software-controlled information processing apparatuses, it will be appreciated that a machine-readable medium (in particular, a non-transitory machine-readable medium) carrying such software, such as an optical disk, a magnetic disk, semiconductor memory or the like, is also considered to represent an embodiment of the present disclosure. In particular, the present disclosure should be understood to include a non-transitory storage medium comprising code components which cause a computer to perform any of the disclosed method(s).

[0233] It will be appreciated that the above description for clarity has described embodiments with reference to different functional units, circuitry and / or processors. However, it will be apparent that any suitable distribution of functionality between different functional units, circuitry and / or processors may be used without detracting from the embodiments.

[0234] Described embodiments may be implemented in any suitable form including hardware, software, firmware or any combination of these. Described embodiments may optionally be implemented at least partly as computer software running on one or more computer processors (e.g. data processors and / or digital signal processors). The elements and components of any embodiment may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the disclosed embodiments may be implemented in a single unit or may be physically and functionally distributed between different units, circuitry and / or processors.

[0235] Although the present disclosure has been described in connection with some embodiments, it is not intended to be limited to those embodiments. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in any manner suitable to implement the present disclosure.

[0236] REFERENCES

[0237] [1] RP-234058, “New SID: Study on solutions for Ambient loT (Internet of Things) in NR”. RAN plenary #102. Edinburgh. December 2023.

[0238] [2] TR38.848. “Study on Ambient loT (Internet of Things) in RAN”.

[0239] [3] “Sensing, Computing, and Communication for Energy Harvesting loTs: A Survey”. Dong Ma, Guohao Lan, Mahbub Hassan, Wen Hu, Sajal K. Das https: / / arxiv.org / absZ1905.03949 [4] Van Huynh, Nguyen, Dinh Thai Hoang, Xiao Lu, Dusit Niyato, Ping Wang, and

[0240] Dong In Kim. "Ambient Backscatter Communications: A Contemporary Survey." IEEE Communications Surveys & Tutorials 20, no. 4 (2018): 2889-2922.

Claims

CLAIMS1. A controller station of a communications system, the controller station having a control interface with one or more carrier wave emitters of the communications system for controlling the one or more carrier wave emitters to transmit carrier wave signals for receipt by one or more tags, wherein the tags are ambient communications devices configured to backscatter carrier wave signals for receipt by the controller station, wherein the controller station comprises: transmitter circuitry for transmitting signals, receiver circuitry for receiving signals, and controller circuitry configured with the transmitter circuitry and receiver circuitry to: execute a first initial access process for a plurality of tags, wherein executing the first initial access process comprises: broadcasting a first control signal for receipt by the plurality of tags, wherein the first control signal indicates resource information for the first initial access process for the plurality of tags; transmitting a first instruction to one or more carrier wave emitters (CWEs) to transmit a first carrier wave signal (CWS) for backscattering by the plurality of tags for the first initial access process; receiving, according to the resource information, backscattered CWS signals from a first set of tags of the plurality of tags; and broadcasting a second control signal for receipt by the first set of tags, wherein the second control signal indicates successful registration of the first set of tags in the first initial access process.

2. The controller station according to claim 1 , wherein the controller station is an infrastructure equipment forming part of a radio network of a wireless communications network.

3. The controller station according to claim 1 , wherein the controller station is an infrastructure equipment of a radio network part of a wireless communications network and the transmitter circuitry is configured to transmit signals to communications devices via a wireless access interface provided by a wireless communications network and the receiver circuitry is configured to receive signals from the communications devices transmitted via the wireless access interface, and the interface with the controller station is formed by the wireless access interface, and the detection station is a wirelesscommunications device which detects the backscattered signals and the controller station receives an indication of the backscattered signals received from the communications device transmitted via the wireless access interface.

4. The controller station according to claim 1 , wherein the interface with the one or more carrier wave emitters is formed by a wireless access interface provided by an infrastructure equipment and a communications device which includes transceiver circuitry configured to transmit and to receive radio signals via the wireless access interface provided by the wireless communications network, the communications device forming part of the one or more carrier wave emitters and the interface of the controller station formed by the infrastructure equipment uses the wireless access interface of the wireless communications network.

5. The controller station according to claim 1 , wherein the one or more carrier wave emitters form part of the controller station.

6. The controller station according to claim 1 , wherein the first control signal indicates that only a particular subset of the plurality of tags are to participate in the first initial access process.

7. The controller station according to claim 6, wherein the particular subset of the plurality of tags comprises devices of a particular type.

8. The controller station according to claim 6, wherein the particular subset of the plurality of tags comprises devices having particular identifiers.

9. The controller station according to claim 6, wherein the particular subset of the plurality of tags is based on a priority level of the plurality of tags.

10. The controller station according to claim 1 , wherein the first control signal indicates a number of pre-scheduled initial access processes.

11. The controller station according to claim 10, wherein the first control signal indicates that tags which successfully register in a first initial access process should not attempt to register in remaining pre-scheduled initial access processes.

12. The controller station according to claim 10, wherein the number of prescheduled initial access processes is based on an estimated number of the plurality of tags.

13. The controller station according to claim 1 , wherein the resource information is based on an estimated number of the plurality of tags.

14. The controller station according to claim 1 , wherein the resource information indicates a set of resource elements to be used for the backscattered CWS signals from the plurality of tags.

15. The controller station according to claim 14, wherein the set of resource elements is indicated as a number of resource elements and a frequency band.

16. The controller station according to claim 1 , wherein the resource information comprises first resource information for a first subset of the plurality of tags, and second resource information for a second subset of the plurality of tags, wherein the first resource information is different to the second resource information, and wherein devices of the first subset of the plurality of tags do not belong to the second subset of the plurality of tags.

17. The controller station according to claim 16, wherein first and second subsets of the plurality of tags comprise devices of different types.

18. The controller station according to claim 17, wherein the first subset comprises passive devices without a device for energy storage, and wherein the second subset comprises semi-passive devices having a device for energy storage.

19. The controller station according to claim 17, wherein the first subset comprises passive devices that backscatter a CWS, and wherein the second subset comprises active devices that actively generate a signal for transmission.

20. The controller station according to claim 18, wherein the first subset of the plurality of tags are assigned a first set of resource elements, and the second subset of the plurality of tags are assigned a second set of resource elements, wherein the first set of resource elements have a smaller absolute frequency than the second set of resource elements.

21. The controller station according to claim 1 , wherein the controller station has a control interface with a plurality of CWEs of the communications system.

22. The controller station according to claim 21 , wherein the first instruction transmitted to the one or more CWEs instructs one or more particular CWEs of the plurality of CWEs based on an estimated geographical distribution of the plurality of tags.

23. The controller station according to claim 21 , wherein the first instruction instructs particular CWEs of the plurality of CWEs to transmit respective first CWSs at different times.

24. The controller station according to claim 21 , wherein the first instruction instructs particular CWEs of the plurality of CWEs to transmit respective first CWSs at different frequencies.

25. The controller station according to claim 21 , further comprising: transmitting a preliminary control signal to the plurality of CWEs, wherein the preliminary control signal instructs the plurality of CWEs to transmit, at different times, respective reference CWSs for receipt by the plurality of tags, and wherein a backscattered signal is received from a particular tag in response to a first CWS signal transmitted by a preferred CWE for the particular tag.

26. The controller station according to claim 1 , wherein the first instruction instructs the one or more CWEs to transmit the first CWS for a pre-defined time duration.

27. The controller station according to claim 1 , wherein the first CWS is an unmodulated single-tone CWS.

28. The controller station according to claim 1 , wherein the backscattered signals from the first set of tags are received on randomised resource elements according to the resource information for the first initial access process.

29. The controller station according to claim 28, wherein the backscattered signals each indicate a random number used to select the resource element on which the backscattered signal was transmitted.

30. The controller station according to claim 1 , wherein the backscattered signals indicate a tag identifier of a tag of the first set of tags from which the respective backscattered signal is received.

31. The controller station according to claim 1 , wherein one or more of the backscattered signals are received via a detector station of the communications system.

32. The controller station according to claim 1 , wherein two or more backscattered signals are received on a particular resource element from two or more respective tags of the plurality of tags, and wherein the second control signal does not indicate successful registration of the two or more tags.

33. The controller station according to claim 32, wherein the second control signal instructs tags which transmitted backscattered signals on the particular resource element to enter a waiting state, in which the tags are to wait for a subsequent initial access process to attempt registration.

34. The controller station according to claim 1 , further comprising storing an association between a resource element on which a particular backscattered signal is received with a particular tag from which the particular backscattered signal is received.

35. The controller station according to claim 1 , wherein the second control signal indicates a state for the one or more tags to enter.

36. The controller station according to claim 35, wherein the state for the one or more tags to enter is based on a number of backscattered signals received by the controller station.

37. The controller station according to claim 35, wherein the state for the one or more tags to enter is based on a number of tags successfully registered in the first initial access process.

38. The controller station according to claim 35, wherein the state for the one or more tags to enter indicated in the second control signal is based on a particular device type of the one or more tags.

39. The controller station according to claim 35, wherein the state for the one or more tags to enter is one or more of: a ready state, an energy harvesting state, and a waiting state.

40. The controller station according to claim 1 , further comprising selectively executing a second initial access process for a CWE of the communications system.

41. The controller station according to claim 40, wherein the selective execution of the second initial access process is based on number of pre-scheduled initial access processes.

42. The controller station according to claim 40, wherein the selective execution of the second initial access process is based on a number of tags in a first set of tags.

43. The controller station according to claim 40, wherein resource information for the second initial access process is different to the resource information for the first initial access process.

44. The controller station according to claim 43, wherein resource information for the second initial access process indicates a different number of resource elements to the resource information for the first initial access process.

45. The controller station according to claim 44, wherein, based on a number of tags in the first set of tags being above a predetermined threshold, the resource information for the second initial access process indicates a greater number of resource elements than the resource information for the first initial access process.

46. The controller station according to claim 43, wherein the resource information for the second initial access process does not include resource elements associated with tags which successfully registered in the first initial access process.

47. The controller station according to claim 40, wherein the resource information for the second initial access process indicates a set of resource elements including a particular resource element on which two or more backscattered signals were received from two or more respective tags of the plurality of tags during the first initial access process.

48. The controller station according to claim 40, wherein the first initial access process and the second initial access process are part of a first group of initial access operations, wherein an identifier for the first group of initial access processes is indicated in one or more control signals of each of the first and second initial access processes; wherein the controller station is further configured to execute a third initial access process, wherein the third initial access process is part of a second group of initial access operations, and wherein an identifier for the second group of initial access processes is indicated in one or more control signals of the third initial access processes.

49. The controller station according to claim 48, wherein the controller station is configured to prevent tags which have successfully registered during the first initial access procedure from attempting to register during the second initial access procedure, and permit tags which have successfully registered during the first initial access procedure to register during the third initial access procedure.

50. The controller station according to claim 1 , further comprising: executing a first multi-tag access process comprising: transmitting a second instruction to one or more CWEs to transmit a second CWS for receipt by registered tags of the plurality of tags; and receiving backscattered signals from one or more of the registered tags on resource elements on which the respective backscattered signals in the first initial access process were received.51 . The controller station according to claim 50, further comprising: selectively executing a second multi-tag access process for a subset of the registered tags from which backscattered signals are not received in the first multi-tag access process, wherein the second multi-tag access process is executed using CWEs which were not utilised in the first multi-tag access process.

52. The controller station according to claim 51 , wherein the second multi-tag access process is selectively executed based on a number of registered tags from which backscattered signals are not received in the first multi-tag access process.

53. The controller station according to claim 51 , comprising executing a plurality of initial access processes and a plurality of multi-tag access processes.

54. The controller station according to claim 53, wherein the plurality of initial access processes and a plurality of multi-tag access processes are sequentially scheduled according to an energy storage capability of respective subsets of tags.

55. The controller station according to claim 53, comprising: executing the first initial access process at a first time, executing a second initial access process at a second time, executing the first multi-tag access process at a third time, and executing a second multitag access process at a fourth time, wherein the second time is after the first time, the third time is after the second time, and the fourth time is after the third time.

56. The controller station according to claim 53, comprising: executing the first initial access process at a first time, executing the first multi-tag access process at a second time, executing a second initial access process at a third time, and executing a second multi-tag access process at a fourth time, wherein the second time is after the first time, the third time is after the second time, and the fourth time is after the third time.

57. A communications system comprising: the controller station according to claim 1 ; and the one or more CWEs, wherein the one or more CWEs are configured to, in response to receiving the first instruction, transmit a CWS for backscattering by the plurality of tags.

58. The communications system of claim 56, further comprising: one or more detector stations configured to receive backscattered signals from the plurality of tags and forward the received backscattered signals to the controller station.

59. Circuitry for a controller station of a communications system, the controller station having a control interface with one or more carrier wave emitters of the communicationssystem for controlling the one or more carrier wave emitters to transmit carrier wave signals for receipt by one or more tags, wherein the tags are ambient communications devices configured to backscatter carrier wave signals for receipt by the controller station, wherein the controller station comprises: transmitter circuitry for transmitting signals, receiver circuitry for receiving signals, and controller circuitry configured with the transmitter circuitry and receiver circuitry to: execute a first initial access process for a plurality of tags, wherein executing the first initial access process comprises: broadcasting a first control signal for receipt by the plurality of tags, wherein the first control signal indicates resource information for the first initial access process for the plurality of tags; transmitting a first instruction to one or more carrier wave emitters (CWEs) to transmit a first carrier wave signal (CWS) for backscattering by the plurality of tags for the first initial access process; receiving, according to the resource information, backscattered CWS signals from a first set of tags of the plurality of tags; and broadcasting a second control signal for receipt by the first set of tags, wherein the second control signal indicates successful registration of the first set of tags in the first initial access process.

60. A method for a controller station of a communications system, the controller station having a control interface with one or more carrier wave emitters of the communications system for controlling the one or more carrier wave emitters to transmit carrier wave signals for receipt by one or more tags, wherein the tags are ambient communications devices configured to backscatter carrier wave signals for receipt by the controller station, the method comprising: executing a first initial access process for a plurality of tags, wherein executing the first initial access process comprises: broadcasting a first control signal for receipt by the plurality of tags, wherein the first control signal indicates resource information for the first initial access process for the plurality of tags; transmitting a first instruction to one or more carrier wave emitters (CWEs) to transmit a first carrier wave signal (CWS) for backscattering by the plurality of tags for the first initial access process;receiving, according to the resource information, backscattered CWS signals from a first set of tags of the plurality of tags; and broadcasting a second control signal for receipt by the first set of tags, wherein the second control signal indicates successful registration of the first set of tags in the first initial access process.

61. A tag configured to backscatter carrier wave signals for receipt by a controller station of a communications system, the tag being an ambient communications device, wherein the tag comprises: energy harvesting circuitry configured to harvest energy from incident carrier wave signals, backscattering circuitry configured to receive incident carrier wave signals and transmit backscattered signals for receipt by the controller station, and controller circuitry configured with the backscattering circuitry to: receive a first control signal from the controller station, wherein the first control signal indicates resource information for a first initial access process for the tag to register with the controller station; backscatter, based on the resource information, an incident carrier wave signal (CWS) from a carrier wave emitter (CWE) for receipt by the controller station using a randomly selected resource element.

62. The tag according to claim 61 , wherein the first control signal indicates that only tags meeting one or more criteria are to participate in the first initial access procedure, and wherein the tag is configured to determine, based on the first control signal, that the tag meets the one or more criteria.

63. The tag according to claim 62, wherein the one or more criteria comprise the tag being a particular type of device.

64. The tag according to claim 62, wherein the one or more criteria comprise the tag having a particular identifier.

65. The tag according to claim 62, wherein the one or more criteria comprise a priority level of the tag.

66. The tag according to claim 61 , wherein the tag is an active device further comprising: energy storage means configured to receive energy from the energy harvesting circuitry, and configured to supply energy to the backscattering and controller circuitry.

67. The tag according to claim 61 , wherein the tag is a passive device, wherein the energy harvesting circuitry is configured to supply energy to the backscattering and controller circuitry.

68. The tag according to claim 61 , wherein the tag is configured to randomly select a resource element based on generating a random number.

69. The tag according to claim 61 , wherein the backscattered CWS includes an identifier for the tag.

70. The tag according to claim 61 , wherein the tag is further configured to: receive a second control signal from the controller station, wherein the second control signal indicates successful registration of the tag in the first initial access process.71 . The tag according to claim 70, wherein the tag is further configured to: determine, based on the second control signal, not to attempt registration in a second initial access procedure.

72. The tag according to claim 71 , wherein the first and second initial access procedures are part of a first group of initial access operations, wherein an identifier for the first group of initial access processes is indicated in one or more control signals of each of the first and second initial access processes.

73. The tag according to claim 72, wherein the tag is further configured to attempt registration in a third initial access procedure, wherein the third initial access process is part of a second group of initial access operations, and wherein an identifier for the second group of initial access processes is indicated in one or more control signals of the third initial access processes.

74. The tag according to claim 70, wherein the tag is further configured to: backscatter a further CWS from a CWE, for receipt by the controller station, wherein the backscattered further CWS utilises the randomly selected resource element.

75. Circuitry for a tag configured to backscatter carrier wave signals for receipt by a controller station of a communications system, the tag being an ambient communications device, wherein the circuitry comprises: energy harvesting circuitry configured to harvest energy from incident carrier wave signals, backscattering circuitry configured to receive incident carrier wave signals and transmit backscattered signals for receipt by the controller station, and controller circuitry configured with the backscattering circuitry to: receive a first control signal from the controller station, wherein the first control signal indicates resource information for a first initial access process for the tag to register with the controller station; backscatter, based on the resource information, an incident carrier wave signal (CWS) from a carrier wave emitter (CWE) for receipt by the controller station using a randomly selected resource element.

76. A method for a tag configured to backscatter carrier wave signals for receipt by a controller station of a communications system, the tag being an ambient communications device, wherein the method comprises: receiving a first control signal from a controller station of a communications system, wherein the first control signal indicates resource information for a first initial access process for the tag to register with the controller station; backscatter, based on the resource information, an incident carrier wave signal (CWS) from a carrier wave emitter (CWE) for receipt by the controller station using a randomly selected resource element.

77. A tag configured to transmit signals for receipt by a controller station of a communications system, the tag being an ambient communications device, wherein the tag comprises: transceiver circuitry configured to receive incident carrier wave signals and transmit signals for receipt by the controller station, and controller circuitry configured with the backscattering circuitry to:receive a first control signal from the controller station, wherein the first control signal indicates resource information for a first initial access process for the tag to register with the controller station; transmit, based on the resource information, a signal for receipt by the controller station using a randomly selected resource element.

78. A controller station of a communications system, the controller station having a control interface with one or more carrier wave emitters of the communications system for controlling the one or more carrier wave emitters to transmit carrier wave signals for receipt by one or more tags, wherein the tags are ambient communications devices, wherein the controller station comprises: transmitter circuitry for transmitting signals, receiver circuitry for receiving signals, and controller circuitry configured with the transmitter circuitry and receiver circuitry to: execute a first initial access process for a plurality of tags, wherein executing the first initial access process comprises: broadcasting a first control signal for receipt by the plurality of tags, wherein the first control signal indicates resource information for the first initial access process for the plurality of tags; receiving, according to the resource information, signals emitted from a first set of tags of the plurality of tags; and broadcasting a second control signal for receipt by the first set of tags, wherein the second control signal indicates successful registration of the first set of tags in the first initial access process.

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