Controller station, radio tag, carrier wave emitter, and associated method of controlling

Abstract

A communications system comprises one or more tags (1), a controller station (4), a plurality carrier wave emitters (3) configured to transmit a radio frequency carrier wave signal to the one or more tags. The controller station is configured to control the carrier wave emitters by transmitting carrier wave emitter control information to the carrier wave emitters to transmit a reference signal by each of the carrier wave emitters at each of a plurality of different times to a tag for determining its location, transmitting tag control information to the tag for controlling the state of the tag to backscatter the reference signal transmitted at each of the different times by each of the carrier wave emitters when the tag is in either a first state or a second state. The controller station then detects the reference signal transmitted by each of the carrier wave emitters at the plurality of the different times, the reference signal being received according to a multipath profile derived from the received reference signal. A state of the tag to backscatter the reference signal when transmitted by each of the carrier wave emitters at the different times changes from the first state to the second state, one of the first state and the second state being more highly reflective to backscatter incident signals than the other of the first state and the second state which is a lower reflective state to backscatter signals, the multipath detected in the more highly reflective state including paths from the reference signal backscattered from the tag, a difference between the detected multipath profiles for the first state and the second state being for use in estimating the location of the tag.

Description

[0001] CONTROLLER STATION, RADIO TAG, CARRIER WAVE EMITTER, AND ASSOCIATED METHOD OF CONTROLLING

[0002] BACKGROUND

[0003] Field of the Disclosure

[0004] The present disclosure relates to detecting radio tags from signals which are backscattered from the tag and more particularly determining a location of the tag from a difference in a multipath profile when the tag is in a reflective state and a low-reflective state. The present disclosure relates to controller stations, carrier wave emitters, radio tags and methods which are configured to estimate a location of the tags. In one example the controller station may be infrastructure equipment of a wireless communications network.

[0005] The present disclosure claims the Paris convention priority from European patent application number EP24167807.7 filed on 28 March 2024, the contents of which are incorporated herein by reference in its entirety.

[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 a t 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. Other devices may not include a sensor or a battery and may only include circuitry which provides an identifier of the device. Such a less complex device needs to transmit the sensor data and / or its identity 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 and in particular determining a location of the tags.

[0009] SUMMARY

[0010] Example embodiments can provide a system comprising a controller station, a plurality of carrier wave emitters which in some examples can be communications devices (UEs) and one or more tags. Embodiments of the present technique utilise a difference in carrier wave multipath profiles to determine a location of a tag which changes its state between a more reflective backscattering state and more absorbing backscattering state. According to one example embodiment, a controller station controls one or more carrier wave emitters in the communications system, the controller station controlling the one or more carrier wave emitters to transmit a reference signal by each carrier wave emitter at each of a plurality of different times to a tag for determining its location, and to detect the reference signal transmitted by each of the carrier wave emitters at the plurality of different times. The reference signal is received according to a multipath profile, wherein a state of the tag to backscatter the reference signal transmitted by each of the carrier wave emitters at each of the different times changes from a first state to a second state. One of the first state and the second state is more highly reflective to backscatter signals than the other of the first state and the second state which is a lower reflective state to backscatter signals, the multipath profile detected in the more highly reflective state including the reference signal backscattered from the tag. A difference between the detected multipath profiles for the first state and the second state can be used to estimate the location of the tag by determining an additional distance between the tag, one or more carrier wave emitters and the controller station in comparison to the distance from the carrier wave emitter to the controller station from a difference in the time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station when the tag is in the reflective state, and from the carrier wave emitter to the controller station when the tag is in the lower reflective state, the difference indicating a distance of the tag and the carrier wave emitter from the identified backscattered paths.

[0011] BRIEF DESCRIPTION OF THE DRAWINGS

[0012] 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:

[0013] Figures 1A and IB 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 reference signals are transmitted by carrier wave emitters in Figure 1A and communications devices (UE) in Figure IB controlled by the infrastructure equipment and backscattered signals are detected in accordance with an example embodiment;

[0014] 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;

[0015] 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;

[0016] Figure 4 is a schematic block diagram illustrating an example of backscattering circuitry which may be employed with example embodiments;

[0017] Figure 5 is a schematic illustration representing an example embodiment in which a signal backscattered from a carrier wave signal transmitted by a carrier wave emitter is detected according to one example;

[0018] Figure 6 is a schematic block diagram illustrating an example arrangement in which a carrier wave emitter is controlled by an infrastructure equipment (gNB) to transmit reference signals and a location of a tag is determined by comparing a multipath profile detected when the tag is in a reflective state and a low-reflective state;

[0019] Figure 7 is a schematic block diagram illustrating how a communications system according to example embodiments can determine a location of a tag by triangulation using an estimate of an additional distance between the tag, one or more carrier wave emitters and the controller station in comparison to the distance from the carrier wave emitter to the controller station by determining the difference in the time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station when the tag is in the reflective state, and from the carrier wave emitter to the controller station when the tag is in the lower reflective state according to example embodiments;

[0020] Figure 8 is a part signaling part process diagram illustrating a determination of an additional distance between the tag, one or more carrier wave emitters and the controller station in comparison to the distance from the carrier wave emitter to the controller station by comparing multipath profiles when the tag is in a reflective state and a low-reflective state;

[0021] Figure 9A is an illustrative representation of physical paths of a reference signal from a carrier wave emitter as detected by a controller station (gNB) when a tag is in a low-reflective state; and Figure 9B is an illustrative representation of physical paths of a reference signal from a carrier wave emitter as detected by a controller station (gNB) when a tag is in a reflective state;

[0022] Figure 10A is an illustrative representation of a multipath profile produced by transmitting a reference signal by a carrier wave emitter as detected by a controller station (gNB) when a tag is in a low-reflective state; and Figure 10B is an illustrative representation of a multipath profile produced by transmitting a reference signal by a controller station (gNB) when a tag is in a reflective state; and Figure IOC is an illustrative representation of a subtracted multipath profile when a multipath profile of Figure 10A is subtracted from the multipath profile of Figure 10B according to example embodiments;

[0023] Figure 11 is a graphical illustration of relationships between a distance of a backscattered path and a determination of a received signal power as a result of a backscattered path; and

[0024] Figure 12 is a graphical illustration of potential tag locations based on an estimated power of scattered reference signals.

[0025] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] Ambient loT

[0027] In release 19 of 3GPP (Rel-19), 3GPP will study Ambient loT (AIoT, A-IoT) [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 provide information by reflecting or backscattering incident radio signals or are powered by radio frequency energy derived from radio signals such as a carrier wave transmitted by a carrier wave emitter (CWE) is shown in Figures 1A and IB, which consider different example configurations of a communication system according to example embodiments. Figures 1A and IB 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” or radio tags, because of the simplicity of the devices. These devices 1 are powered by and / or backscatter radio signals 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 1A, 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 a reference signal or carrier wave signal 2 transmitted by the CWE 3. In a second example, wireless communications devices or UEs 7 act as CWEs and transmit a reference signal or carrier wave signal 2, which is backscattered by the devices (tags) 1 as backscattered signals 5 from the tags 1, which are detected by a controller station (gNB) 4. Therefore, according to example embodiments, a controller station (gNB) 4 controls the carrier wave emitters 3 or UE 7 to transmit the reference or carrier wave signals 2, and the backscattered signals 5 are detected by the controller station 4. In some examples, a separate detection station or reader (not shown in Figures 1A and IB) may be deployed which detects the backscattered signals 5 and 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 formed between the gNB 4 and the detection device. In some examples a UE 7 may act as a detection station.

[0028] According to the arrangements of Figures 1A and IB, the tags 1 may modulate the reflected or backscattered signal 5 with information which is detected by the gNB 4 or a UE 7 acting as a detection station.

[0029] As shown in Figures 1A and IB 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 reference signal or CW 2 as will be explained below. The gNB 4 therefore has an interface 6 to the CWE 3. In the example of Figure IB a communications device or UE 7 which operates with a wireless communications network of which the gNB 4 receives control information from the gNB or controller station 4 via the wireless access interface provided by the gNB 4. 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.

[0030] The CWE 3 can be a standalone device or can be part of another network node and as in Figure IB is a UE 7, such as a legacy UE or smartphone. In this case, the UE can be controlled to send a reference signal or a carrier wave signal. It is also possible for the AIoT device to transmit data in the uplink by backscattering another signal (for example the DL signal from the gNB).

[0031] In some examples, such as the example of Figure IB, the backscattered signal 5 may be received by a separate detection station 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, the architecture of a typical 5G or New Radio (NR) wireless communications network will now be described with reference to Figures 2 and 3. As will be explained below, embodiments of the present technique provide techniques for assisting to identify a location of the tags 1.

[0032] 5G New Radio (NR) Wireless Communications System

[0033] 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) 41, 42 by a connection interface represented as a line 16. Each of the TRPs 10 is arranged to transmit and receive signals via a wireless access interface within a radio frequency bandwidth available to the wireless communications network. Thus, within a range for performing radio communications via the wireless access interface, each of the TRPs 10, forms a cell of the wireless communications network as represented by a dashed line 12. As such, wireless communications devices 7 which are within a radio communications range provided by the cells 12 can transmit and receive signals to and from the TRPs 10 via the wireless access interface. Each of the distributed units 41, 42 are connected to a central unit (CU) 40 (which may be referred to as a controlling node) via an interface 46. The central unit 40 is then connected, via an interface 60, to a core network 20 which may contain all other functions required for communicating data to and from the wireless communications devices and the core network 20. The core network 20 may be connected to other radio networks and infrastructure equipment. The elements of the wireless access network shown in Figure 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 rele ant standards.

[0034] As explained, the TRPs 10 of Figure 2 may in part have a corresponding functionality to a gNB 4, 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.

[0035] In terms of broad top-level functionality, the central unit 40 and associated DUs 41, 42 / TRPs 10 may be broadly considered to provide functionality corresponding to the gNB 4 of Figure 1. The term network infrastructure equipment / 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 41, 42 and / or TRPs 10. Communications devices 7 are represented in Figure 2 within the coverage area of respective communication cells 12. These communications devices 7 may thus exchange signalling with the CU 40 via the TRP 10 associated with their respective communications cells 12.

[0036] 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.

[0037] 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 7 within a cell 12 formed by the TRP 10. As shown in Figure 3, an example UE 7 is shown to include a corresponding wireless transmitter 49, wireless receiver 48 and a controller or controlling processor 44 which is configured to control the transmitter 49 to transmit signals representing uplink data to the wireless communications network via the wireless access interface formed by the TRP 10 and the receiver 48 to receive downlink data as signals transmitted by the transmitter 30 in accordance with the conventional operation. The transmitters 30, 49 and the receivers 32, 48 (as well as other transmitters, receivers and transceivers described in relation to examples and embodiments of the present disclosure) may include radio frequency filters and amplifiers as well as signal processing components and devices in order to transmit and receive radio signals in accordance, for example, with the 5G / NR standard. The controllers 34, 44 (as well as other controllers described in relation to examples and embodiments of the present disclosure) may be, for example, a microprocessor, a CPU, or a dedicated chipset, etc., configured to carry out instructions which are stored on a computer readable medium, such as a non-volatile memory. The processing steps described herein may be carried out by, for example, a microprocessor in conjunction with a random access memory, operating according to ins ructions stored on a computer readable medium.

[0038] The interface 46 between the DU 42 and the CU 40 is known as the F 1 interface which can be a physical or a logical interface. The Fl interface 46 between CU and DU may operate in accordance with specifications 3GPP TS 38.470 and 3GPP TS 38.473 and, for example, may be formed from a fibre optic or other wired high bandwidth connection. In one example, the connection 16 from the TRP 10 to the DU 42 is via fibre optic. The connection between a TRP 10 and the core network 20 can be generally referred to as a backhaul, which comprises the interface 16 from the TRP 10 to the DU 42 and the Fl interface 46 from the DU 42 to the CU 40.

[0039] RF Incident Energy

[0040] 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.

[0041] 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.

[0042] 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 AIoT system.

[0043] 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.

[0044] Another disadvantage is that, to reduce the power consumption of a receiver that operates on incident RF energy, a low power waveform / 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. 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],

[0045] Backscattering Principle

[0046] 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.

[0047] 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 70 including a matching network comprising two load impedances 72, 74 an antenna 76, represented by an antenna impedance, and a switch 78 and an IC 82. The incident RF wave is represented by an oscillator 80.

[0048] There are two aspects of power that are relevant to the Ambient loT device:

[0049] • Absorbed power. This is the power that is energy harvested and can be used to drive the circuits within the tag.

[0050] • Reflected power. This is the power that is reflected as a backscattered signal.

[0051] Given the antenna and load impedances denoted as Za= Ra+ jRaand Z„ = Rn+ jXn, n = 1,2, respectively, the reflection coefficient corresponding to each state is expressed as where * denotes the complex conjugate operation. Note that Figure 4 shows the antenna impedance Zaas 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, e.g., n = 1. Z, = Za* 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).

[0052] The absorbed power can be calculated as

[0053] Pin,n = Pavail(l " |fn ) where Pavaildenotes 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], 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.

[0054] Given PaVaii- the average power absorbed by the device can be calculated as

[0055] Where pn,n=i,2 denote the ratio of time duration for each impedance state; = p2holds if the probability of each impedance equals to the other (this also means the 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).

[0056] CW Emitter

[0057] Example embodiments address the case that the signal from the tag is backscattered. The carrier-wave emitter (or CW emitter / 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 88. The backscattered signal is backscattered on the CW signal by the backscattering module 88, which may have the structure shown in Figure 4. The tag 1 includes an energy harvesting module 84, which converts energy of the carrier wave signal into power to drive a microcontroller 86 and the backscattering module 88.

[0058] The tag can be powered by non-RF energy sources, such as via solar power. The tag can also / 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).

[0059] The CW emitter devices may take the following forms:

[0060] • Base station. The base station (e.g. gNodeB) acts as the CW emitter.

[0061] • 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.

[0062] • 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. 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 AIoT downlink based on ambient RF power, for example power that is received directly from the gNB.

[0063] 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.

[0064] Example embodiments utilise an arrangement in which carrier wave emitters can transmit different types of signal, including:

[0065] • Carrier wave signal to allow the tag to backscatter or harvest energy. This can be a single tone or multi- tone signal

[0066] • Reference signal. The reference signal can be a multi-tone signal in the form of an LTE / NR reference signal (sounding reference signal (SRS), demodulation reference signal (DMRS) etc)

[0067] The protocol for Ambient loT operation can be based on a command / response type of protocol. A detection station, which might be a gNB or a separate reader, sends a downlink command signal with a command to the tag. For example, the downlink command signal could indicate to the tag that it should respond with its identity (such as an identity number). The downlink command signal could indicate some further aspect of how the tag should respond. For example, the downlink command signal may indicate an amount of frequency shift that should be applied to the response signal, or may indicate a time at which the response signal should be transmitted. Based on the downlink command signal, the tag responds with a backscattered signal, where the backscattered signal is backscattered on the carrier wave signal.

[0068] To assist in the explanation below, the following acronyms are used:

[0069] CWS: Carrier wave signal. This is the signal or power that is sent by a carrier wave emitter in order to provide a signal from which the tag can send a backscattered signal.

[0070] CWE: carrier wave emitter. This is an entity that transmits a carrier wave signal. The CWE can be a standalone device or could be co-located with the reader.

[0071] System Description

[0072] An A-IoT system illustrating example embodiments which is shown in Figures 1A and IB and described above is shown in Figure 6 as a simplified representation, in which parts also shown in Figures 1A and IB have the same numerical references. For the example shown in Figure 6, there are three CWEs 3, each of which is scheduled by the gNB as a controller station 4 for a CW transmission to the A-IoT device 1 (‘Tag’). The device 1 also receives a command from the gNB 4 and responds accordingly, e.g., standby, data transmission and reflection in a manner known by the gNB.

[0073] In a general indoor scenario, A-IoT devices (tags) 1 are deployed to attach to objects for various purposes, e.g., inventory, environment monitoring, etc. Tags 1 are connected to a cellular network which is served by a single gNB or reader 4. Since the tags can only conduct backscattering communications, bi-static topology has been configured to enhance the communication range; this is realized by the deployment of multiple CWEs which transmit CWS to the tag and enable the backscattering at the tag.

[0074] The location of the CWEs 3 is known to the gNB 4 while the location of the tag 1 is unknown and to be determined by the gNB.

[0075] Both the CWEs 3 and the tag 1 receive commands from the gNB 4 and respond based on the command.

[0076] Capability of CWEs - CWEs 3 can receive, process, and transmit OFDM-based multi-tone signals. The CWS that CWEs transmit is in the form of an unmodulated single-tone signal, which can be generated by only transmitting through a single OFDM subcarrier or other ways compatible to OFDM based transmission.

[0077] The CWEs can support accurate time synchronization with gNB 4, which is an aspect which can be used to aid in the accuracy of time of flight (ToF) measurements at the gNB side. The CWE 3 can achieve an accurate time synchronisation by either synchronising to a synchronisation signal block (SSB) or other synchronisation signals such as positioning reference signal (PRS) transmitted by the gNB on the Uu interface or synchronising over a backhaul interface, such as a fibre optic interface.

[0078] Capability of tags - tags 1 cannot actively generate the signal for transmission due to their low-complexity nature. Typically tags 1 do not 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.

[0079] Apart from the basic functionalities, e.g., data transmission, registration, and identification, etc., a tag 1 is also able to be controlled, based on the command received from gNB on the R2D link, via its chip 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 explained above with reference to Figures 4 and 5, for example a constant absorption / reflection state, etc. (i.e. high reflection and low / no reflection states can be achieved by changing the reflection ratios).

[0080] 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.

[0081] 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. ToF -based triangulation techniques (such as multi-RTT, OTDOA and UTDOA) in legacy systems rely on accurate timing ability at the UE (the device being triangulated) and this accurate timing is simply not possible for an Ambient loT tag.

[0082] Embodiments of the present technique can provide an arrangement for locating a tag that uses backscattering communication without requiring the tag to have sophisticated synchronization and signal processing circuitry. According to example embodiments there is provided a system comprising a controller station, a plurality of carrier wave emitters which in some examples can be communications devices (UEs) and one or more tags. Although the location of the controller station and the carrier wave emitters is known, a location of the tags is unknown and the present technique utilises a difference in multipath profiles to determine a location of a tag which changes its state between a more reflective backscattering state and more absorbing backscattering state. When a UE acts as a carrier wave emitter, its location can be determined by the controller station (gNB) using conventional GPS / GNSS positioning technology or 3 GPP-based positioning techniques or other means.

[0083] According to one example embodiment, a controller station controls one or more carrier wave emitters in a communications system, the controller station including controller circuitry configured to control a transmitter circuitry and a receiver circuitry to transmit carrier wave emitter control information to the one or more carrier wave emitters for controlling the one or more carrier wave emitters to transmit a reference signal by each carrier wave emitter at each of a plurality of different times to a tag for determining its location, and to detect the reference signal transmitted by each of the carrier wave emitters at the plurality of different times. The reference signal is received, from which the multi-path profile of the transmission channel can be determined. A state of the tag to backscatter the reference signal transmitted by each of the carrier wave emitters at each of the different times is changed from a first state to a second state. One of the first state and the second state is more highly reflective to backscatter incident signals than the other of the first state and the second state which is a lower reflective state to backscatter signals. The multipath profile detected in the more highly reflective state includes the reference signal backscattered from the tag whilst the multipath profile detected in the less / no reflective state does not. Therefore, by processing the difference between the detected multipath profiles for the first state and the second state the location of the tag can be estimated. Detection of a time difference of arrival between the direct path of the reference signal from the carrier wave emitter to the controller station or gNB and the path from the carrier wave emitter, to the tag and then the controller station (gNB), which is a main path of the backscattered signal produced when the tag is in a reflective or more highly reflective state provides an indication of an additional distance between the tag, one or more carrier wave emitters and the controller station in comparison to the distance from the carrier wave emitter to the controller station. By repeating the backscattered path detection process from a plurality of carrier wave emitters, a location of the tag can be determined by triangulation.

[0084] According to example embodiments a carrier wave emitter 3 or UE 7 transmits a reference signal (such as SRS) that reflects off an Ambient loT tag and is received by the reader / gNB 4. The gNB 4 can then measure the multipath profile of the received reference signal. The tag’s reflection state is then changed and another reference signal is transmitted, leading to a second multipath profile. The difference in the two multipath profiles is used to determine the additional distance from the CWE / UE via the tag to the gNB compared to the distance between the CWE and gNB. By repeating this process for multiple CWEs / UEs in known locations, a set of additional path distances can be measured. This set of path distances is used to multi-laterate the tag’s location. The backscattered signal from the tag may be further reflected from objects in the environment, leading to the difference in the two multipath profiles consisting of more than a single path. The first path of the difference in the two multipath profiles relates to the distance from the tag to the base station and can be used for triangulation. The other paths of the difference in the two multipath profiles relate to reflection of the backscattered signal from other objects in the environment and can be ignored for the purposes of triangulation. The base station hence needs to process the difference in the two multipath profiles in order to determine a path that is associated with the distance between the tag and the gNB. For example, the base station can determine a first significant path in the difference in the two multipath profiles that is above a threshold for use in the triangulation / multi-lateration process.

[0085] ToF acquisition - The ToF (time of flight) related to each CWE is defined as the time between the CW signal transmission at each CWE, and the resulting backscattered signal reception at the gNB. Depending on the presence of a CWS, the ToF can be further categorized into the CWE-to-gNB ToF (also called as ‘direct-link’ ToF) and the CWE-to-tag-to-gNB ToF (also called as ‘backscattered-link’ ToF).

[0086] Both types of ToF can be measured by transmitting a reference signal from the CWE. Since the gNB has the knowledge of the reference signal, it can correlate the received signal with the known reference signal pattern to derive the ToF.

[0087] More specifically, the direct-link ToF is derived from the multipath profile measured from the reference signal correlation. The multipath profile measured for the direct link when the backscattered signal of the interested tag is not present can be used to exclude the effect of most of the background multipath when the backscattered signal is present. This would help in determining a more accurate ToF for the backscattered signal link. Based on the detected change, the backscattered-link ToF can therefore be derived.

[0088] Note that the measurement of direct-link and backscattered-link ToF needs to be conducted within the channel coherence time during which the background multipath profile is expected not to change much.

[0089] Firstly, the gNB commands the tag to enter its low reflection mode / state. Then it commands the CWE to transmit the CW reference signal. The gNB measures a multipath profile A during which the tag is not backscattering. Secondly, the gNB commands the tag to engage its high reflection mode. Then it commands the CWE to transmit the CW reference signal. The gNB then measures a multipath profile B during which the tag is backscattering. If the two measurements were carried out within the coherence time of the channel, then by subtracting multipath profile A from multipath profile B, we are left only with a multipath profile due to the backscattered signal. This is explained in more detail below.

[0090] Localisation of the tag can be based on ToF - Given the ToF measured for the entire additional link, i.e., CWE-to- tag-to-gNB link, the following mathematical expression holds for the w-th CWE, d + dn= c x tn(Eq. 1)

[0091] Where d denotes the tag-gNB distance and dndenotes the CWE-tag distance from the n-th CWE to the tag; e{l, . . . , Ajwhere N > 3 and tnis a total time to travel the distance d + dn, that is from the CWE to the tag and from the tag to the gNB. N = 3 is considered for illustrative purposes in Figure 6.

[0092] A relationship between d and dnas described in (Eq. 1) implies that the potential location of the tag is on an ellipse whose foci are the location of the gNB and the CWE n; the tag’s location can be determined by finding the common intersection between different ellipses 92 which correspond to different CWEs as illustrated in Figure 7. As shown in Figure 7 an intersection of the different ellipses 92 based on the distances di, d2 and d provides an estimate of a location of the tag 1 given a known location of the CWEs 3. Computation of this intersection also known as triangulation is illustrated in Figure 7 as an illustration of a localization process with a trilateration method (in general a multi-lateration can be applied, where the multi-lateration uses more than three nodes); the process relies on the calculation of the sum of two distances, i.e., CWE-tag and tag-gNB distance. ToF is measured by the gNB for each scheduled CWE.

[0093] A part process, part signaling flow diagram is shown in Figure 8, which provides a summary of the technique performed by example embodiments, further details of which are explained below. As shown in Figure 8, the following operations are performed:

[0094] • CWE1 is instructed to transmit SRS

[0095] • Tag is instructed to apply a low reflection state. The multipath profile based on the SRS received with the tag in this low reflection state is measured by the gNB.

[0096] • Tag is instructed to apply a high reflection state. The multipath profile based on the SRS received with the tag in this high reflection state is measured by the gNB.

[0097] • The gNB measures the difference between the multipath profiles associated with CWE 1 in order to estimate a path difference, PD1

[0098] • CWE2 is instructed to transmit SRS

[0099] • Tag is instructed to apply a low reflection state. The multipath profile based on the SRS received with the tag in this low reflection state is measured by the gNB.

[0100] • Tag is instructed to apply a high reflection state. The multipath profile based on the SRS received with the tag in this high reflection state is measured by the gNB.

[0101] • The gNB measures the difference between the multipath profiles associated with CWE2 in order to estimate a path difference, PD2

[0102] • Based on the path differences PD1, PD2 and the known locations of CWE1, CWE2 and the gNB, the gNB multilaterates the location of the tag. Further path differences associated with further CWE can be used to determine a more accurate location of the tag

[0103] As will be appreciated further measurements may be made from other CWEn which increases an accuracy of a determined location of a tag. As will be appreciated in order to perform an estimate of a location of the tag, at least three estimates of distances from three CWEs is required in order to perform triangulation.

[0104] The above example sequence as illustrated in Figure 8 works in a case in which there is a line of sight between CWE and gNB. To be able to take the differences between the two multipath profiles in some cases, in other example embodiments, it is helpful if the gNB knows when the CWE starts SRS transmission in each case. For example, in a case in which there is no LOS between CWE and gNB; and CWE-gNB 'direct path' is longer than CWE-tag-gNB path. Therefore, CWE1 is commanded to stop transmitting SRS after multipath profile is measured with tag in low reflective state. Then, tag is commanded to enter high reflective state, then CWE 1 is commanded to restart SRS transmission In the example case above, there can be other time references (datum) for use in calculating the difference between the multipath profiles other than a time of arrival of the CWE-gNB 'direct path', for example the time the command to transmit SRS is sent to the CWE or end of slot in which the command is sent etc

[0105] Determining the Path Difference from the Multipath Profiles

[0106] Figure 9A shows a scenario with a tag 1 in a low-reflective state and Figure 9B shows a corresponding scenario with the tag 1 in a reflective state. For the illustrative example shown in Figure 9A and 9B, solid lines 100 illustrate transmission paths which make up a multipath profile. There is also a direct transmission path A as illustrated by a dotted line 102 and an indirect transmission path B in which a reference signal transmitted to the tag 1 via a first part of the indirect transmission path 104b is reflected or backscattered via a second part of the indirect transmission path 104b as shown in Figure 9B. However, the second part 104b of the transmission path B is not present when the tag is in a non-reflective state as illustrated in Figure 9A and represented by a X 106.

[0107] When the tag is in a reflective state (right), the reference signal transmitted by the CWE is reflected by the tag and received by the gNB 4. In the low-reflective state (left), the reference signal is not reflected by the tag 1 and path ‘B’ does not exist. In both cases, there is a strong LOS direct path between the CWE and the gNB. This path 102 is labelled ‘A’. There are also environment paths 100, where the reference signal bounces off scatterers in the environment and is received by the gNB to form with the direct and indirect paths 102, 104 a multipath profile.

[0108] The corresponding multipath profiles are illustrated in Figure 10A for the tag in a low-reflective state and Figure 10B for a reflective state. Figure 10B shows that there is an additional path, ‘B’, in the multipath profile when the tag is in a reflective state, which is backscattered from the tag, that is CWE -> tag -> gNB.

[0109] According to example embodiments, the gNB can align the reflected state and non-reflected state profiles based on the location of the direct path, ‘A’, and then subtract the multipath profiles, as shown in Figure 10C. The time of reception of the direct path ‘A’ forms a time reference. The distance of the remaining multipath profile ‘B’ from the time reference is related to the extra path distance for the indirect path CWE -> tag -> gNB compared to the direct path CWE -> gNB. This path difference can be used in the procedure for the localisation of the tag, as described in the main idea above.

[0110] Note that when there is a line of sight (LOS) between CWE and gNB, there is no need for synchronisation between the CWE and the gNB since the gNB can determine the time difference based on a difference in multipath timings. The time difference does not depend on the absolute time at which a CWE sent the reference signal. The lack of requirement for accurate CWE synchronisation makes this technique more robust to CWE imperfections and allows for lower complexity CWE implementation. Current 3 GPP positioning techniques assume a line of sight (LOS) path component for multi-lateration purposes.

[0111] When there is no line of sight (NLOS conditions) between the CWE and gNB, it is preferred that the gNB and CWE are synchronised in order to determine the timing position of the multipath profile path component associated with the tag in its reflective state relative to the time at which the SRS was transmitted. For example, the CWE can synchronise to the gNB using known means (e.g. using the SSB transmitted by the gNB) and either (1) indicate the time at which it transmitted SRS (or UL reference signal) relative to the synchronised time from the gNB or (2) transmit the SRS (or UL reference signal) at a time instructed by the gNB. In either case, the gNB would be able to determine the time of the multipath profile path component associated with the tag in its reflective state based on the arrival time of that path and the known transmission time of the SRS (or UL reference signal).

[0112] Note that there may be some requirement for the CWE to transmit such that its reference signal arrives within the cyclic prefix duration at the gNB / reader. This optional requirement is simply part of the normal operation of the UL and is controlled by procedures such as timing advance. gNB instructs which CWE to transmit a reference signal

[0113] A single CWE is indicated to transmit the reference signal. At a different time, a different CWE can be configured to transmit the reference signal. The multipath measurements from the different reference signal transmissions can be used to determine the path differences pertaining to this CWE that are used for triangulation.

[0114] Different reference signal sequences can be applied to different CWE and the CWEs can all transmit at the same time. The gNB / reader will then correlate the different reference signals in order to determine the multipath profiles associated with the different CWEs. The gNB / reader can then determine the multipath profiles (and hence path differences) associated with the different CWEs in parallel.

[0115] Number of CWE transmitting reference signals controlled by the gNB

[0116] The gNB can control the number of CWEs that transmit reference signals for the purpose of tag localisation. The number of CWEs can be determined based on the required location accuracy and the network power consumption.

[0117] Nature of reference signals

[0118] Possible reference signals for the CWE / UE to transmit include:

[0119] SRS (sounding reference signals)

[0120] DMRS (demodulation reference signals)

[0121] PRACH (physical random access channel) preambles

[0122] In general, the reference signal does not necessarily need to be one of the existing (in LTE / NR) reference signals, provided that the reference signal can be used by the gNB / reader to estimate a multipath profile. Use of an existing reference signal however has the advantage of minimising specification and gNB / reader implementation changes. gNB instructs the tag how it should modulate its reflection state

[0123] The gNB will know which tag it is trying to locate. For example, it may be known that a certain tag exists from an initial inventory procedure. The gNB then wishes to locate that tag. The gNB can hence address a specific tag for the purposes of determining its location. The gNB can hence send an instruction to the particular tag to modulate its reflection state. Modulation of the reflection state means changing the reflection state from a high reflection state to a low reflection state or vice versa.

[0124] Reflection state directly controlled

[0125] The gNB can control the tag to switch its reflection state to a known state. For example, the gNB can control the tag to switch to a first reflection state and control the CWE to transmit a reference signal. The gNB then makes a measurement of the multipath profile. The gNB then controls the CWE to stop transmission of the reference signal. The gNB then controls the tag to use a second reflection state and again controls the CWE to transmit a reference signal. The gNB can then determine a second multipath profile. The differences in the multipath profiles can then be used to estimate the path difference associated with the tag. In other example embodiments, in addition to controlling the CWE to transmit and to stop transmitting the reference signal, the gNB controls the CWE to transmit the reference signal for a time period T secs in the knowledge that it would take less than or equal to T secs for it to measure the multipath profile. Then after the CWE has been transmitting reference signal for T secs, it will stop transmitting.

[0126] Other tags told to maintain a stable reflection state Tags other than the target tag that are not being located are instructed to maintain a stable reflection state or instructed not to change their reflection state for a duration Tm seconds, where Tm is the timespan of the localisation procedure for the target tag. The other tags can be set in either of the first and second reflection states, provided that their reflection states do not change during the timespan of the localisation procedure for the target tag. As long as the reflection state of all other tags remains stable, whether it is an off or on state, for the process of localization of the target tag, reflections from any of them will contribute equally to the measurement of the 'direct-link multipath profile' and the ‘backscatter multipath profile’ , which will not affect the detection of the multipath profile change introduced by the backscattered link of the target tag for which localisation is being performed.

[0127] One reflection state may be more stable than another reflection state and that more stable reflection state is preferred. For example the switch that controls the load impedance might default to a stable location when power is removed from the switch. In this case, that “no power” switch location would define the stable reflection state.

[0128] Tag modulates its reflection state gNB instructs tag to modulate its reflection state at a known rate

[0129] The rate can be a function of the SNR, coherence time of the channel, number of devices to be located etc.

[0130] Reflection state modulation rate based on SNR

[0131] A better multipath profile can be determined if the multipath profile is integrated for a period of time. A longer period of time is necessary at lower SNRs. The gNB may hence measure the SNR of the multipath path component associated with the reflected path and determine the time period for which the tag should be in each reflection state: if the multipath path component SNR is low, a longer reflection state dwell time would be chosen.

[0132] The multipath path component SNR could be measured from known techniques from 3 GPP Release- 18 positioning technology or by any other means.

[0133] Reflection state modulation rate based on coherence time

[0134] In order to determine the path difference with and without the tag, it is necessary to measure the multipath profile with the tag in a low and then a high reflection state. The difference in the multipath profiles indicates the backscattered path from the tag. For this scheme to work, the baseline multipath profile must be static / stationary for each reflection state. A multipath profile is considered to be static for the duration of the coherence time of the radio propagation channel.

[0135] Hence, the reflection state modulation rate is determined such that the sum of the times for the tag to be in the first reflection state and the second reflection state is less than the coherence time of the channel.

[0136] Note that a legacy gNB would estimate the coherence time of the channel in any case (it needs to know the coherence time for configuring its channel estimation circuitry). Hence, the channel coherence time is known to the gNB.

[0137] Reflection state modulation rate based on number of devices that need to be located

[0138] If many tags need to be located within one channel coherence time cycle, the time that can be devoted to the localisation of each tag reduces. Hence, the reflection state modulation rate can be based on the number of devices that need to be located.

[0139] Reflection state modulation rate based on mix of factors In reality, the gNB has to consider conflicting requirements when determining a reflection state modulation rate. The reflection state modulation rate can hence consider more than one of the factors for determining the modulation rate from the above embodiments.

[0140] Signalling of reflection state modulation parameters

[0141] In some examples, the R2D signal that controls the reflection state of the tag includes the dwell time during which the tag must maintain one reflection state. The signal can alternatively indicate a start time and a stop time for which the tag must maintain the reflection state. The timings can be relative to the time at which the R2D command is received by the tag. gNB instructs tag to modulate its reflection state according to a sequence

[0142] Applying different sequences (or different cover codes) to the different tags allows multiple tags to be located at the same time. The gNB / reader can assign a sequence of reflection states to be used by the tag, for example when the localisation procedure for the tag is initiated. By detecting the sequences and the multipath profiles, the gNB receiver can determine which multipath profiles are associated with which tags. The application of different cover codes to the reflection state modulation of different tags hence allows multiple tags to be located simultaneously.

[0143] The different sequences applied to the different tags can be cover codes, so that the gNB instructs each tag to modulate its reflection state according to a cover code which may be different between tags. The signals reflected by the tag (e.g. an SRS signal sent from a CWE) hence have a cover code applied to them. By processing the received sequences with the cover codes, it is possible to determine the multipath profile associated with each tag, allowing multiple tags to be located at the same time. gNB instructs tag to modulate its reflection state with a frequency shift

[0144] In addition (or alternatively) to the methods described elsewhere in B3.x, the tag can be instructed to frequency shift its backscattered (reflected) signal. The tag can frequency shift its reflected signal by rapidly switching between load impedance states at the rate of the frequency shift. Frequency shifting different tags by different amounts allows multiple tags to be located simultaneously. gNB observes a tag exists on straight line between CWE and gNB based on modulating response

[0145] When the tag is not on the direct line between the CWE and gNB, there are two paths on the multipath profile: the direct path from the CWE to gNB and the path from CWE -> tag -> gNB. This two path channel can be readily observed and the path difference determined. When the tag is on the direct line between CWE and gNB, the CWE -> gNB and CWE -> tag -> gNB path lengths are the same and there is no path difference. In this case, it is not possible to distinguish between the cases where (1) the tag lies on this line, and (2) the tag is not responding.

[0146] However, when the tag changes its reflection state, the power received by the gNB changes at the rate of the reflection state change. Hence, by observing a main path whose magnitude fluctuates at the rate of the reflection state change, the gNB can determine that the tag is located on a direct line between CWE and gNB. This information can be used in the multilateration process for locating the tag.

[0147] Determining that a tag has lost charge and gone to sleep

[0148] The localisation process consumes some power at the tag. The tag has a finite energy store. Once the energy store is depleted, the tag is no longer able to change its reflection state. The gNB needs to understand when the tag has lost charge as it can then discard any multipath measurements when the tag is not changing its reflection state. The gNB can determine that the tag has lost charge using one or more of the following embodiments:

[0149] Multipath profile at gNB does not change

[0150] When the gNB thinks that the tag should be changing its reflection state but the multipath profile received by the gNB does not change, the gNB can estimate that the tag has lost charge and hence terminate the localisation procedure. The gNB can still use the multipath profiles that were obtained prior to termination. Of course, if the tag is on a direct line between the OWE and gNB then the multipath component associated with the OWE - gNB (i.e. the direct path) would change as the tag cycles between reflective and low-reflective states. gNB requests response from tag

[0151] The gNB can send a R2D command signal that requires a (backscattered) response from the tag. If the tag responds, the gNB knows that the tag is still charged and responsive. Hence, the gNB can send these keep alive messages to determine that the tag is still charged and still participating in the localisation procedure.

[0152] Response to tag losing charge

[0153] If the tag has lost charge, the OWE can be instructed to transmit a dedicated carrier wave, allowing the tag to charge.

[0154] Note that other embodiments described in this report just assume that the CWE sends a reference signal. It may not be possible for the tag to charge based on this reference signal alone due either to the nature of the signal (wideband vs narrowband) or due to the power level at which the reference signal is transmitted. There may hence be a need for dedicated CW to be sent at certain times, as per this embodiment.

[0155] Signalling to LMF

[0156] The gNB / reader may not be the entity that finally determines the tag location. The gNB / reader may signal information to an LMF (location management function) and the LMF may determine the tag location. To facilitate this procedure, the gNB may send one or more of the following pieces of information to the LMF: gNB location

[0157] CWE location(s)

[0158] UE location(s) - see embodiment below in which a UE acts as a CWE

[0159] Multipath profiles associated with a tag being in each of the reflection states

[0160] Path difference measurements

[0161] UEs (e.g. smartphones) are told to transmit the reference signal rather than CWE

[0162] Embodiments above have been described in relation to CWEs transmitting the reference signal. However, any node can transmit the reference signal. The important aspect is that the tag switches into a different reflection / impedance state while the reference signal is being transmitted.

[0163] UE transmits UL reference signals

[0164] A UE transmits the UL reference signals. The UE can be any UE that is capable of transmitting UL reference signals and does not necessarily need to be a UE that has explicit A-IoT functionality. For example, a legacy smartphone UE can be used to transmit the UL reference signals. It is necessary to know the location of the UE in order to triangulate the tag. The UE location can be either known a priori or the UE location can be signalled or discerned. A location of the UE can be known a priori, for example, UEs may be deployed in known locations within an Ambient loT service area for the purposes of tag localisation. A location of the UE can be signalled by, for example, the UE signalling its geographic location based on GPS / GNSS measurements or the network determining the UE location by a legacy 3 GPP positioning technique.

[0165] UE transmits SRS

[0166] The UE can be instructed to transmit SRS. The SRS are subjected to the different reflection states of the tag at different times as explained above and the gNB can measure the multipath profile both with and without the tag reflecting.

[0167] UE transmits DMRS

[0168] The UE can be instructed to transmit DMRS. The DMRS may be transmitted as part of some other transmission, such as a PUSCH or a PUCCH. Indeed, the gNB can just measure the multipath profile based on any UE in a known location transmitting a PUSCH. The toggling reflection state of the tag will not affect the demodulation (by the gNB) of the PUSCH from the UE since the channel with the reflection path from the tag affects both the DMRS and the PUSCH itself, because the PUSCH is decoded based on a channel estimate for a channel that contains a reflector.

[0169] Search to find a suitable UE

[0170] There may be many potential UEs that could be used as part of this procedure. The gNB can refine its choice of involved UEs via an algorithm.

[0171] For example, the gNB can choose some initial UEs to use to triangulate the tag. This triangulation can lead to a rough position estimate of the tag (the choice of UEs for the triangulation may not be ideal leading to the tag location estimate being rough). Based on the rough estimate of tag location, the gNB can choose other UEs that are well placed relative to the rough tag location to take part in a process to determine a more refined tag location. Note that “well placed” could mean either that the chosen UEs are close to the approximate tag location or that they are in advantageous locations for example that the UEs are spaced 120 degrees apart which will lead to an intersection of ellipses with large angles, increasing accuracy as shown for example in Figure 7.

[0172] Use of RSRP Additionally in the Multilateration Process

[0173] In addition to the ToF, reference signal received power (RSRP) can also contribute to the tag localization. Specifically, the RSRP of the backscattered link can be derived by subtracting the direct- link signal (obtained in the slot where the interested tag does not backscatter signal) from the received signal which is a superposition of both direct-link and backscattered-link signals in the time domain.

[0174] The following equation defines the signal power received at the gNB with the CW being transmitted from the CWE n where a denotes the ratio incurred by various factors, e.g., transmitted signal power, transmitting / receiving antenna gain, channel gain and reflection coefficient, etc.

[0175] Generally, the gNB has knowledge about cr; based on this, it can further calculate Eq. 2 a relationship between d and dncan be used to form a function of hyperbola (first quadrant only); and by jointly solving it with the Eq. 1, we can find the possible pairs of the distances , which are depicted as the intersections of two curves in Figure 11, e.g., the intersections can be found at d = 17.5, dn= 53 or d = 53, dn= 17.5.

[0176] The physical essence of the intersections is the possible distance combinations for dnand d. Based on the RSRP and ToF measurement, it is not obvious which pair of distances indicates the actual distances between the tag and the CWE (dn) or the tag and gNB (d). Nevertheless, , two pairs of circles could be drawn to illustrate the potential locations of the tag, with radii corresponding to the possible value of d or dn,.. as shown in Fig. 12 (the axes of this figure are the 2D coordinates of entity locations, corresponding to the distances shown in Fig. 11). The circles represent possible tag locations based on tag distance from CWE or gNB. The solid lines in Fig. 12 represent the possible locations of the tag based on the hypothesis that d = 17.5, dn= 53. The dashed lines in Fig. 12 represent the possible locations of the tag based on the hypothesis that d = 53, dn= 17.5. The intersections of the circles drawn with the same dash type hence represent possible locations of the tag. While two possible tag locations are identified, it may be possible for the gNB to eliminate one of the two possible tag locations (or prefer one of the possible tag locations over the other), for example by using angle of arrival information or by eliminating impossible tag locations based on known a priori information (for example, if the tag is known to be in a warehouse and two possible tag locations are (1) in the warehouse and (2) in a car park, the gNB can reject the possible tag location in the car park and choose the possible tag location in the warehouse).

[0177] Although it is not shown in the Figures 11 and 12, the same process can be repeated for different CWEs and the final tag location of the tag could be determined as the common intersection between the circles drawn for different CWEs. This will further refine the location of the tag and remove the ambiguity relating to whether the tag is located at the first possible location shown in Fig. 12 or the second possible location shown.

[0178] The current 3GPP assumption is that the tag will be located only by its proximity to a gNB / reader. If the tag is in the service area of a gNB / reader, it is considered to be local to that gNB / reader. This existing method does not provide an accurate location of the tag.

[0179] Positioning techniques in earlier 3 GPP releases rely on the tag sending a reference signal at a known time.

[0180] • The technique described in the above example embodiments does not require the tag to send a reference signal, it just requires the tag to change its reflective state.

[0181] • Existing positioning techniques measure ToF based on a signal timing relative to the base station timing. This technique is based on the difference in the timing of multipath components.

[0182] Further example embodiments of the present technique are defined in the following numbered claims: Paragraph 1. A controller station for controlling carrier wave emitters in a communications system, the controller station comprising receiver circuitry configured to receive signals, transmitter circuitry configured to transmit signals, and controller circuitry configured to control the transmitter circuitry and the receiver circuitry, wherein the controller circuitry is configured with the transmitter circuitry and the receiver circuitry to transmit carrier wave emitter control information to a plurality of carrier wave emitters for controlling the carrier wave emitters to transmit a reference signal by each of the one or more carrier wave emitters at each of a plurality of different times to a tag for determining its location, to transmit tag control information to the tag, for controlling the state of the tag to backscatter the reference signal transmitted at each of the different times by each of the carrier wave emitters in either a first state or a second state, and to detect the reference signal transmitted by each of the carrier wave emitters at the plurality of the different times, the reference signal being received according to a multipath profile derived from the received reference signal, wherein a state of the tag to backscatter the reference signal when transmitted by each of the carrier wave emitters at the different times changes from the first state to the second state, one of the first state and the second state being more highly reflective to backscatter incident signals than the other of the first state and the second state which is a lower reflective state to backscatter signals, the multipath detected in the more highly reflective state including paths from the reference signal backscattered from the tag, a difference between the detected multipath profiles for the first state and the second state being for use in estimating the location of the tag.

[0183] Paragraph 2. A controller station of paragraph 1, wherein the controller circuitry is configured with the transmitter circuitry and the receiver circuitry to detect the reference signal transmitted at each of the plurality of the different times by each of the plurality of carrier wave emitters, and to determine a different multipath profile from each reference signal received which is transmitted by each of the plurality of carrier wave emitters at each of the plurality of different times, and, to identify a difference in the multipath profiles between when the tag is in a first state and when the tag is in a second state from the reference signals transmitted by each of the carrier wave emitters, the difference in the multipath profiles including a difference in a time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station when the tag is in the reflective state, and from the carrier wave emitter to the controller station when the tag is in the lower reflective state, the difference being for use in determining an additional distance between the tag, one or more carrier wave emitters and the controller station in comparison to the distance from the carrier wave emitter to the controller station.

[0184] Paragraph 3. A controller station of paragraph 1 or 2, wherein the reference signal is transmitted by each of the plurality of carrier wave emitters periodically.

[0185] Paragraph 4. A controller station of any of paragraphs 1, 2 or 3, wherein the totality of different times for transmission of the reference signal is less than a coherence time of the radio channel via which the reference signal is received for use in deriving both multipath profiles.

[0186] Paragraph 5. A controller station of any of paragraphs 2 to 4, wherein the controller circuitry is configured to estimate an additional distance between the tag, one or more carrier wave emitters and the controller station in comparison to the distance from the carrier wave emitter to the controller station by using a detected reference signal received on a direct path from each of the one or more carrier wave emitters when the tag is in the first state and the second state as a datum, aligning and then subtracting the multipath profile detected when the tag is in the first state from the multipath profile detected when the tag is in the second state to identify the paths of the reference signal backscattered from the tag with reference to the datum, and determining the difference in the time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station when the tag is in the reflective state, and from the carrier wave emitter to the controller station when the tag is in the lower reflective state, the difference indicating an additional distance between the tag, one or more carrier wave emitters and the controller station in comparison to the distance from the carrier wave emitter to the controller station from the identified backscattered paths. Paragraph 6. A controller stations of paragraph 5, wherein the controller circuitry is configured to estimate a location of the tag by determining a path in the difference in the multipath profiles which is associated with a distance between the carrier wave emitter, the tag and the controller station, determining an additional time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station from the determined path, determining a locus of possible locations of the tag with respect to each of a plurality of carrier wave emitters and the controller station, based on the additional times of flight determined from the reference signals transmitted by each of the carrier wave emitters at different times, , and triangulating a position of the tag with respect to a known location of the carrier wave emitters and the controller station.

[0187] Paragraph 7. A controller station of any of paragraphs 5 or 6, wherein the controller circuitry is configured with the receiver station to detect a reference signal received power, RSRP, with which the reference signal transmitted at each of the plurality of the different times by each of the plurality of carrier wave emitters is received, a difference between the RSRP received when the reference signal is transmitted by each of the plurality of carrier wave emitters at the different times being representative of the difference in the time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station when the tag is in the reflective state, and from the carrier wave emitter to the controller station when the tag is in the lower reflective state.

[0188] Paragraph 8. A controller station of paragraph 7, wherein the RSRP is detected from a main path of the multipath profiles detected at the different times, the main path representing a direct-link path between the carrier wave emitter and the controller station, there being no difference in time for the main path with a difference in RSRP, when the tag is on the direct-link path between the carrier wave emitter and the controller station.

[0189] Paragraph 9. A controller station of any of paragraphs 1 to 8, wherein the controller circuitry is configured to transmit a representation of the detected multipath profiles to a location management function for the location management function to determine a location of the tag from the detected multipath profiles.

[0190] Paragraph 10. A controller station of paragraph 9, wherein the controller circuitry is configured to transmit to the location management function one or more of a representation of a location of the controller station, a location of the one or more carrier wave emitters, a difference in RSRP determined for the multi-path profiles detected at the different times of transmission by each of the carrier wave emitters and path difference measurements of the multipath profiles.

[0191] Paragraph 11. A controller station of any of paragraphs 1 to 10, wherein the controller circuitry is configured with the transmitter circuitry and the receiver circuitry to detect each of the different reference signals transmitted at each of the plurality of the different times by each of the plurality of carrier wave emitters, a different multipath profile being estimated from the received signal for each of the different reference signals that were transmitted at each of the plurality of different times at which the different reference signals were transmitted by each of the plurality of carrier wave emitters , the tag control information controlling the state of the tag to backscatter the reference signal transmitted at each of the different times by each of the carrier wave emitters in either the first state or the second state to produce the different multipath profiles for each different reference signal transmitted by each of the carrier wave emitters, the difference in the multipath profiles being for use in determining a distance of the tag from each of the plurality of carrier wave emitters for determining the location of the tag.

[0192] Paragraph 12. A controller station of paragraph 11, wherein one or more of the carrier wave emitters transmit the different reference signals which at least partially overlap time. Paragraph 13. A controller station of paragraph 11 or 12, wherein the controller circuitry is configured to select the plurality of carrier wave emitters from a set of available carrier wave emitters and transmit the carrier wave emitter control information to the selected plurality of carrier wave emitters from the set.

[0193] Paragraph 14. A controller station of any of paragraphs 1 to 13, wherein the controller station is an infrastructure equipment of a radio network part of a wireless communications network and the reference signal transmitted by the transmitter circuitry is a sounding reference signal, SRS, configured for a wireless access interface provided by the wireless communications network.

[0194] Paragraph 15. A controller station of any of paragraphs 1 to 13, wherein the controller station is an infrastructure equipment of a radio network part of a wireless communications network and the reference signal transmitted by the transmitter circuitry is a demodulation reference signal, DMRS, configured for a wireless access interface provided by the wireless communications network.

[0195] Paragraph 16. A controller station of any of paragraphs 1 to 13, wherein the controller station is an infrastructure equipment of a radio network part of a wireless communications network and the reference signal transmitted by the transmitter circuitry is a Physical Random Access Channel, PRACH, preamble configured for a wireless access interface provided by the wireless communications network.

[0196] Paragraph 17. A controller station of any of paragraphs 1 to 16, wherein the controller circuitry is configured with the transmitter circuitry and the receiver circuitry to transmit tag control information to one of the tags for determining a location of the tag, the tag control information configuring the tag to control the state of the tag to backscatter the reference signal at each of the different times in either of the first state or the second state.

[0197] Paragraph 18. A controller station of paragraph 17, wherein the tag control information and the carrier wave emitter control information configure the tag to be in the first state when the reference signal is transmitted at a first time by the at least one carrier wave emitter and to be in the second state when the reference signal is transmitted at a second time by the at least one carrier wave emitter.

[0198] Paragraph 19. A controller station of paragraph 17, wherein the controller circuitry is configured with the transmitter circuitry to transmit tag control information to at least one other tag to control the at least one other tag to remain in the same first or second backscatter reflection state for the plurality of different times when the reference signal is transmitted.

[0199] Paragraph 20. A controller station of paragraph 17, wherein the tag control information configures the tag to change from the first state to the second state at a modulation rate indicated by the tag control information. Paragraph 21. A controller station of paragraph 20, wherein the modulation rate identifies a first time period in which the tag should be in the first state and a second time period in which the tag should be in the second state, a length of first time period and a second time period being determined in accordance with a signal-to-noise ratio with which the reference signals are detected by the controller station.

[0200] Paragraph 22. A controller station of paragraph 20, wherein the modulation rate identifies a first time period in which the tag should be in the first state and a second time period in which the tag should be in the second state, a sum of a temporal length of the first time period and the second time period being less than a coherence time of the radio channel through which the reference signals are detected.

[0201] Paragraph 23. A controller station of paragraph 20, wherein the tag control information includes a detection period during which the tag is configured to change from the first state to the second state at the modulation rate, the detection period being determined in accordance with a number of tags from which a location is to be determined.

[0202] Paragraph 24. A controller station of paragraph 20, wherein the modulation rate identifies a first time period in which the tag should be in the first state and a second time period in which the tag should be in the second state, the modulation rate including the first and the second time periods, which are determined in accordance with a combination of a signal-to-noise ratio with which the reference signals are detected by the controller station, a coherence time of the radio channel through which the reference signals are detected and a detection period during which the tag is configured to change from the first state to the second state at the modulation rate, the detection period being determined in accordance with a number of tags from which a location is to be determined. Paragraph 25. A controller station of paragraph 17, wherein the tag control information includes a detection period during which the tag is configured to change from the first state to the second state at the modulation rate, and the tag control information includes an indication of a start of the detection period with respect to when the tag control information is received.

[0203] Paragraph 26. A controller station of paragraph 17, wherein the tag control information configures the tag to change from the first state to the second state according to a sequence, from which a location of the tag can be determined contemporaneously with other tags.

[0204] Paragraph 1. A controller station of paragraph 17, wherein the tag control information configures the tag to change from the first state to the second state at a modulation rate indicated by the tag control information, the modulation rate frequency shifting the backscattered signal reflected by the tag by switching between load impedances.

[0205] Paragraph 28. A controller station of paragraph 1 wherein the frequency shift is different for each tag. Paragraph 29. A controller station of any of paragraphs 1 to 16, wherein the controller circuitry is configured with the receiver circuitry to identify an increase in a detected power of a main path of the paths of the different multi-path profiles which are detected, which is the same main path for each of the different multipath profiles detected at each of the plurality of different times at which the reference signal is transmitted by the carrier wave emitter, the identified path being a direct path from the carrier wave emitter and the controller station on which the tag is located. Paragraph 30. A controller station of any of paragraphs 1 to 16, wherein the controller circuitry is configured with the receiver circuitry to identify that one or more of the different multi-path profiles which are detected have paths which do not change between each of the one or more different multi-path profiles detected at each of the one or more different times at which the reference signal is transmitted by the carrier wave emitter, the identified one or more multi-path profiles which do not change indicating that the tag is no longer operating to backscatter the reference signal.

[0206] Paragraph 31. A controller station of paragraph 30, wherein the controller circuitry is configured with the transmitter circuitry to instruct the carrier wave emitter to stop transmitting the reference signal to the tag. Paragraph 32. A controller station of paragraph 30, wherein the controller circuitry is configured with the transmitter circuitry to send a command to the carrier wave emitter to start transmitting the reference signal to the tag at a first time and to stop transmitting the reference signal at a second time after the first time.

[0207] Paragraph 33. A controller station of any of paragraphs 1 to 16, wherein the controller circuitry is configured with the receiver circuitry and the transmitter circuitry to transmit a command signal to request a response from the tag, and if a response is received from the tag in response to the command signal, determining that the tag is still operating, or if no response is received from the tag in response to the command signal, determining that the tag is not operating.

[0208] Paragraph 34. A controller station of any of paragraphs 1 to 16, wherein the controller circuitry is configured with the receiver circuitry and the transmitter circuitry to transmit a control signal to the carrier wave emitter indicating that the carrier wave emitter should transmit a dedicated carrier wave to the tag to ensure the tag can respond by backscattering the reference signal. Paragraph 35. A controller station of any of paragraphs 1 to 34, 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, an interface with the controller station being formed by the wireless access interface.

[0209] Paragraph 36. A controller station of paragraph 35, wherein one or more of the at least one carrier wave emitters are wireless communications devices which transmits the reference signal to the tag under the control of the infrastructure equipment.

[0210] Paragraph 37. A controller station of paragraph 35, wherein the reference signal transmitted by the wireless communications device as one of the carrier wave emitters is a synchronisation reference signal, SRS.

[0211] Paragraph 38. A controller station of paragraph 35, wherein the reference signal transmitted by the wireless communications device as one of the carrier wave emitters is a demodulation reference signal, DMRS.

[0212] Paragraph 39. A controller station of paragraph 36, wherein the wireless communications device is configured to transmit DMRS.

[0213] Paragraph 40. A controller station of paragraph 35, wherein the controller circuitry is configured with the receiver circuitry and the transmitter circuitry of infrastructure equipment forming the controller station of a wireless communications network to estimate a location of the tag by selecting a first set of wireless communications devices based on an estimated location of the tag, determining a distance of the tag from each of the wireless communications devices of the first set acting as carrier wave emitters by subtracting multipath profiles detected from reference signals transmitted by each of the wireless communications devices of the first set, and triangulating a position of the tag with respect to a known location of the controller station and of the wireless communications devices of the first set.

[0214] Paragraph 41. A controller station of paragraph 40, wherein the controller circuitry is configured with the receiver circuitry and the transmitter circuitry of infrastructure equipment forming the controller station of a wireless communications network to estimate a location of the tag by selecting a second set of wireless communications devices based on the estimated location of the tag from the wireless communications devices of the first set, the second set being in a better position to the tag than the first set, determining a difference in the time of flight of the reference signal from the wireless communications devices of the second set to the tag and to the controller station when the tag is in the reflective state, and from the wireless communications devices of the second set to the controller station when the tag is in the lower reflective state to determine a locus of possible locations of the tag with respect to each of the wireless communications devices of the second set acting as carrier wave emitters based on the additional times of flight determined from the reference signals transmitted by each of the wireless communications devices of the second set, and triangulating a position of the tag with respect to a known location of the controller station and of the wireless communications devices of the second set.

[0215] Paragraph 42. A controller station of paragraph 41, wherein the second set of wireless communications devices is in a better position relative to the tag by being closer than the first set.

[0216] Paragraph 43. A controller station of paragraph 42, wherein the second set of wireless communications devices is in a better position relative to the tag based on an angle to the tag compared to the first set. Paragraph 44. A controller station of paragraphs 41, 42 or 43, wherein one or more of the wireless communications devices of the second set also forms part of the first set.

[0217] Paragraph 45 A controller station of paragraph 35, wherein the interface with the one or more carrier wave emitters is formed by a wireless access interface provided by the 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.

[0218] Paragraph 46. A radio tag, comprising an antenna, controller circuitry connected to the antenna, and backscattering circuitry connected to the antenna and to the controller circuitry, wherein the controller circuitry is configured to receive tag control information from a controller station for configuring an operation of the radio tag, and in response to the tag control information, to control the backscattering circuitry to be in a first state in which the backscattering circuitry in combination with the antenna are configured to more highly backscatter incident reference signals than a second state in which the backscattering circuitry and the antenna are configured to have a lower reflective state to backscatter signals than the first state.

[0219] Paragraph 47. A radio tag of paragraph 45, wherein controller circuitry is configured by the tag control information to control the state of the tag to backscatter the reference signal at different times in either of the first state or the second state, when the reference signal is transmitted by a carrier wave emitter.

[0220] Paragraph 48. A radio tag of paragraph 46, wherein controller circuitry is configured by the tag control information to control the state of the tag to be in the first state when the reference signal is transmitted at a first time by the at least one carrier wave emitter and to be in the second state when the reference signal is transmitted at a second time by the at least one carrier wave emitter.

[0221] Paragraph 49. A radio tag of paragraph 46, wherein controller circuitry is configured by the tag control information to control the state of the tag to remain in the same first or second backscatter reflection state for the plurality of different times when the reference signal is transmitted.

[0222] 50. A radio tag of paragraph 46, wherein controller circuitry is configured by the tag control information to control the state of the tag to change from the first state to the second state at a modulation rate indicated by the tag control information.

[0223] Paragraph 51. A radio tag of paragraph 50, wherein the modulation rate identifies a first time period in which the tag should be in the first state and a second time period in which the tag should be in the second state, the modulation rate including the first and the second time periods, which are determined in accordance with a combination of a signal-to-noise ratio with which the reference signals are detected by the controller station, a coherence time of the radio channel through which the reference signals are detected and a detection period during which the tag is configured to change from the first state to the second state at the modulation rate, the detection period being determined in accordance with a number of tags from which a location is to be determined. Paragraph 52. A radio tag of paragraph 50, wherein the tag control information includes a detection period during which the tag is configured to change from the first state to the second state at the modulation rate, and the tag control information includes an indication of a start of the detection period with respect to when the tag control information is received. Paragraph 53. A radio tag of paragraph 50, wherein the tag control information configures the tag to change from the first state to the second state according to a sequence representing a cover code, from which a location of the tag can be determined contemporaneously with other tags.

[0224] Paragraph 54. A radio tag of paragraph 50, wherein the tag control information configures the tag to change from the first state to the second state at a modulation rate indicated by the tag control information, the modulation rate frequency shifting the backscattered signal reflected by the tag by switching between load impedances.

[0225] Paragraph 55. A radio tag of paragraph 54, wherein the frequency shift is different for each tag.

[0226] Paragraph 56. A carrier wave emitter operating in a communications system with a controller station and one or more tags, the carrier wave emitter comprising receiver circuitry configured to receive signals, transmitter circuitry configured to transmit signals, and controller circuitry configured to control the transmitter circuitry and the receiver circuitry, wherein the controller circuitry is configured with the transmitter circuitry and the receiver circuitry to receive control information for controlling the transmitter circuitry and in accordance with the control information, to transmit a reference signal at each of a plurality of different times for determining a location of a tag. Paragraph 57. A method of controlling carrier wave emitters by a controller station in a communications system, the method comprising transmitting carrier wave emitter control information to a plurality of carrier wave emitters for controlling the carrier wave emitters to transmit a reference signal by each of the carrier wave emitters at each of a plurality of different times to a tag for determining its location, transmitting tag control information to the tag for controlling the state of the tag to backscatter the reference signal transmitted at each of the different times by each of the carrier wave emitters when the tag is in either a first state or a second state, and detecting the reference signal transmitted by each of the carrier wave emitters at the plurality of the different times, the reference signal being received according to a multipath profile derived from the received reference signal, wherein a state of the tag to backscatter the reference signal when transmitted by each of the carrier wave emitters at the different times changes from the first state to the second state, one of the first state and the second state being more highly reflective to backscatter incident signals than the other of the first state and the second state which is a lower reflective state to backscatter signals, the multipath detected in the more highly reflective state including paths from the reference signal backscattered from the tag, a difference between the detected multipath profiles for the first state and the second state being for use in estimating the location of the tag.

[0227] Paragraph 58. A method of paragraph 57, wherein the detecting the reference signal transmitted by each of the carrier wave emitters at the plurality of the different times comprises detecting the reference signal transmitted at each of the plurality of the different times by each of the plurality of carrier wave emitters, determining a different multipath profile from each reference signal received which is transmitted by each of the plurality of carrier wave emitters at each of the plurality of different times, and identifying a difference in the multipath profiles between when the tag is in a first state and when the tag is in a second state from the reference signals transmitted by each of the carrier wave emitters, the difference in the multipath profiles including a difference in a time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station when the tag is in the reflective state, and from the carrier wave emitter to the controller station when the tag is in the lower reflective state, the difference being for use in determining a distance of the tag from each of the plurality of carrier wave emitters for determining the location of the tag.

[0228] Paragraph 59. A method of paragraph 57 or 58, wherein the reference signal is transmitted by each of the plurality of carrier wave emitters periodically.

[0229] Paragraph 60. A method of any of paragraphs 57, 58 or 59, wherein the totality of different times for transmission of the reference signal is less than a coherence time of the radio channel via which the reference signal is received for use in deriving both multipath profiles.

[0230] Paragraph 61. A method of any of paragraphs 57 to 60, wherein the identifying the difference in the multipath profiles between when the tag is in a first state and when the tag is in a second state from the reference signals transmitted by each of the carrier wave emitters comprises using a detected reference signal received on a direct path from each of the carrier wave emitters when the tag is in the first state and the second state as a datum, aligning and then subtracting the multipath profile detected when the tag is in the first state from the multipath profile detected when the tag is in the second state to identify the paths of the reference signal backscattered from the tag with reference to the datum, and determining the difference in the time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station when the tag is in the reflective state, and from the carrier wave emitter to the controller station when the tag is in the lower reflective state, the difference indicating an additional distance between the tag, one or more carrier wave emitters and the controller station in comparison to the distance from the carrier wave emitter to the controller station.

[0231] Paragraph 62. A method of paragraph 61 , comprising estimating a location of the tag by determining a path in the difference in the multipath profiles which is associated with a distance between the carrier wave emitter, the tag and the controller station, determining an additional time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station from the determined path, determining a locus of possible locations of the tag with respect to each of a plurality of carrier wave emitters and the controller station, based on the additional times of flight determined from the reference signals transmitted by each of the carrier wave emitters at different times, , and triangulating a position of the tag with respect to a known location of the carrier wave emitters and the controller station.

[0232] 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 claims, the disclosure may be practiced otherwise than as specifically described herein.

[0233] 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). 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 these 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. E dinburgh. 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, M ahbub Hassan, Wen Hu, Sajal K. Das https: / / arxiv.org / abs / 1905.03949

[0240] [4] Van Huynh, Nguyen, Dinh Thai Hoang, Xiao Lu, Dusit Niyato, Ping Wang, and Dong In Kim. "Ambient Backscatter Communications: A Contemporary Survey." IEEE Communications Surveys & Tutorials 20, no. 4 (2018): 2889-2922.

Claims

CLAIMS1. A controller station for controlling carrier wave emitters in a communications system, the controller station comprising receiver circuitry configured to receive signals, transmitter circuitry configured to transmit signals, and controller circuitry configured to control the transmitter circuitry and the receiver circuitry, wherein the controller circuitry is configured with the transmitter circuitry and the receiver circuitry to transmit carrier wave emitter control information to a plurality of carrier wave emitters for controlling the carrier wave emitters to transmit a reference signal by each of the one or more carrier wave emitters at each of a plurality of different times to a tag for determining its location, to transmit tag control information to the tag, for controlling the state of the tag to backscatter the reference signal transmitted at each of the different times by each of the carrier wave emitters in either a first state or a second state, and to detect the reference signal transmitted by each of the carrier wave emitters at the plurality of the different times, the reference signal being received according to a multipath profile derived from the received reference signal, wherein a state of the tag to backscatter the reference signal when transmitted by each of the carrier wave emitters at the different times changes from the first state to the second state, one of the first state and the second state being more highly reflective to backscatter incident signals than the other of the first state and the second state which is a lower reflective state to backscatter signals, the multipath detected in the more highly reflective state including paths from the reference signal backscattered from the tag, a difference between the detected multipath profiles for the first state and the second state being for use in estimating the location of the tag.

2. A controller station of claim 1, wherein the controller circuitry is configured with the transmitter circuitry and the receiver circuitry to detect the reference signal transmitted at each of the plurality of the different times by each of the plurality of carrier wave emitters, and to determine a different multipath profile from each reference signal received which is transmitted by each of the plurality of carrier wave emitters at each of the plurality of different times, and, to identify a difference in the multipath profiles between when the tag is in a first state and when the tag is in a second state from the reference signals transmitted by each of the carrier wave emitters, the difference in the multipath profiles including a difference in a time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station when the tag is in the reflective state, and from the carrier wave emitter to the controller station when the tag is in the lower reflective state, the difference being for use in determining an additional distance between the tag, one or more carrier wave emitters and the controller station in comparison to the distance from the carrier wave emitter to the controller station.

3. A controller station of claim 1, wherein the reference signal is transmitted by each of the plurality of carrier wave emitters periodically.

4. A controller station of claim 1, wherein the totality of different times for transmission of the reference signal is less than a coherence time of the radio channel via which the reference signal is received for use in deriving both multipath profiles.

5. A controller station of claim 2, wherein the controller circuitry is configured to estimate an additional distance between the tag, one or more carrier wave emitters and the controller station in comparison to the distance from the carrier wave emitter to the controller station by using a detected reference signal received on a direct path from each of the one or more carrier wave emitters when the tag is in the first state and the second state as a datum, aligning and then subtracting the multipath profile detected when the tag is in the first state from the multipath profile detected when the tag is in the second state to identify the paths of the reference signal backscattered from the tag with reference to the datum, and determining the difference in the time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station when the tag is in the reflective state, and from the carrier wave emitter to the controller station when the tag is in the lower reflective state, the difference indicating an additional distance between the tag, one or more carrier wave emitters and the controller station in comparison to the distance from the carrier wave emitter to the controller station from the identified backscattered paths.

6. A controller stations of claim 5, wherein the controller circuitry is configured to estimate a location of the tag by determining a path in the difference in the multipath profiles which is associated with a distance between the carrier wave emitter, the tag and the controller station, determining an additional time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station from the determined path, determining a locus of possible locations of the tag with respect to each of a plurality of carrier wave emitters and the controller station, based on the additional times of flight determined from the reference signals transmitted by each of the carrier wave emitters at different times, , and triangulating a position of the tag with respect to a known location of the carrier wave emitters and the controller station.

7. A controller station of any of claim 5, wherein the controller circuitry is configured with the receiver station to detect a reference signal received power, RSRP, with which the reference signal transmitted at each of the plurality of the different times by each of the plurality of carrier wave emitters is received, a difference between the RSRP received when the reference signal is transmitted by each of the plurality of carrier wave emitters at the different times being representative of the difference in the time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station when the tag is in the reflective state, and from the carrier wave emitter to the controller station when the tag is in the lower reflective state.

8. A controller station of claim 7, wherein the RSRP is detected from a main path of the multi-path profiles detected at the different times, the main path representing a direct-link path between the carrier wave emitter and the controller station, there being no difference in time for the main path with a difference in RSRP, when the tag is on the direct-link path between the carrier wave emitter and the controller station.

9. A controller station of claim 1, wherein the controller circuitry is configured to transmit a representation of the detected multipath profiles to a location management function for the location management function to determine a location of the tag from the detected multipath profiles.

10. A controller station of claim 9, wherein the controller circuitry is configured to transmit to the location management function one or more of a representation of a location of the controller station, a location of the one or more carrier wave emitters, a difference in RSRP determined for the multi-path profiles detected at the different times of transmission by each of the carrier wave emitters and path difference measurements of the multipath profiles.

11. A controller station of claim 1, wherein the controller circuitry is configured with the transmitter circuitry and the receiver circuitry to detect each of the different reference signals transmitted at each of the plurality of the different times by each of the plurality of carrier wave emitters, a different multipath profile being estimated from the received signal for each of the different reference signals that were transmitted at each of the plurality of different times at which the different reference signals were transmitted by each of the plurality of carrier wave emitters , the tag control information controlling the state of the tag to backscatter the reference signal transmitted at each of the different times by each of the carrier wave emitters in either the first state or the second state to produce the different multipath profiles for each different reference signal transmitted by each of the carrier wave emitters, the difference in the multipath profiles being for use in determining a distance of the tag from each of the plurality of carrier wave emitters for determining the location of the tag.

12. A controller station of claim 11, wherein one or more of the carrier wave emitters transmit the different reference signals which at least partially overlap time.

13. A controller station of claim 11, wherein the controller circuitry is configured to select the plurality of carrier wave emitters from a set of available carrier wave emitters and transmit the carrier wave emitter control information to the selected plurality of carrier wave emitters from the set.

14. A controller station of claim 1, wherein the controller station is an infrastructure equipment of a radio network part of a wireless communications network and the reference signal transmitted by the transmitter circuitry is a sounding reference signal, SRS, configured for a wireless access interface provided by the wireless communications network.

15. A controller station of claim 1, wherein the controller station is an infrastructure equipment of a radio network part of a wireless communications network and the reference signal transmitted by the transmitter circuitry is a demodulation reference signal, DMRS, configured for a wireless access interface provided by the wireless communications network.

16. A controller station of claim 1, wherein the controller station is an infrastructure equipment of a radio network part of a wireless communications network and the reference signal transmitted by the transmitter circuitry is a Physical Random Access Channel, PRACH, preamble configured for a wireless access interface provided by the wireless communications network.

17. A controller station of claim 1, wherein the controller circuitry is configured with the transmitter circuitry and the receiver circuitry to transmit tag control information to one of the tags for determining a location of the tag, the tag control information configuring the tag to control the state of the tag to backscatter the reference signal at each of the different times in either of the first state or the second state.

18. A controller station of claim 17, wherein the tag control information and the carrier wave emitter control information configure the tag to be in the first state when the reference signal is transmitted at a first time by the at least one carrier wave emitter and to be in the second state when the reference signal is transmitted at a second time by the at least one carrier wave emitter.

19. A controller station of claim 17, wherein the controller circuitry is configured with the transmitter circuitry to transmit tag control information to at least one other tag to control the at least one other tag to remain in the same first or second backscatter reflection state for the plurality of different times when the reference signal is transmitted.

20. A controller station of claim 17, wherein the tag control information configures the tag to change from the first state to the second state at a modulation rate indicated by the tag control information.

21. A controller station of claim 20, wherein the modulation rate identifies a first time period in which the tag should be in the first state and a second time period in which the tag should be in the second state, a length of first time period and a second time period being determined in accordance with a signal-to-noise ratio with which the reference signals are detected by the controller station.

22. A controller station of claim 20, wherein the modulation rate identifies a first time period in which the tag should be in the first state and a second time period in which the tag should be in the second state, a sum of a temporal length of the first time period and the second time period being less than a coherence time of the radio channel through which the reference signals are detected.

23. A controller station of claim 20, wherein the tag control information includes a detection period during which the tag is configured to change from the first state to the second state at the modulation rate, the detection period being determined in accordance with a number of tags from which a location is to be determined.

24. A controller station of claim 20, wherein the modulation rate identifies a first time period in which the tag should be in the first state and a second time period in which the tag should be in the second state, the modulation rate including the first and the second time periods, which are determined in accordance with a combination of a signal-to-noise ratio with which the reference signals are detected by the controller station, a coherence time of the radio channel through which the reference signals are detected and a detection period during which the tag is configured to change from the first state to the second state at the modulation rate, the detection period being determined in accordance with a number of tags from which a location is to be determined.

25. A controller station of claim 17, wherein the tag control information includes a detection period during which the tag is configured to change from the first state to the second state at the modulation rate, and thetag control information includes an indication of a start of the detection period with respect to when the tag control information is received.

26. A controller station of claim 17, wherein the tag control information configures the tag to change from the first state to the second state according to a sequence, from which a location of the tag can be determined contemporaneously with other tags.

1. A controller station of claim 17, wherein the tag control information configures the tag to change from the first state to the second state at a modulation rate indicated by the tag control information, the modulation rate frequency shifting the backscattered signal reflected by the tag by switching between load impedances.

28. A controller station of claim 1 wherein the frequency shift is different for each tag.

29. A controller station of claim 1, wherein the controller circuitry is configured with the receiver circuitry to identify an increase in a detected power of a main path of the paths of the different multi-path profiles which are detected, which is the same main path for each of the different multipath profiles detected at each of the plurality of different times at which the reference signal is transmitted by the carrier wave emitter, the identified path being a direct path from the carrier wave emitter and the controller station on which the tag is located.

30. A controller station of claim 1, wherein the controller circuitry is configured with the receiver circuitry to identify that one or more of the different multi-path profiles which are detected have paths which do not change between each of the one or more different multi-path profiles detected at each of the one or more different times at which the reference signal is transmitted by the carrier wave emitter, the identified one or more multi-path profiles which do not change indicating that the tag is no longer operating to backscatter the reference signal.

31. A controller station of claim 30, wherein the controller circuitry is configured with the transmitter circuitry to instruct the carrier wave emitter to stop transmitting the reference signal to the tag.

32. A controller station of claim 30, wherein the controller circuitry is configured with the transmitter circuitry to send a command to the carrier wave emitter to start transmitting the reference signal to the tag at a first time and to stop transmitting the reference signal at a second time after the first time.

33. A controller station of claim 1, wherein the controller circuitry is configured with the receiver circuitry and the transmitter circuitry to transmit a command signal to request a response from the tag, and if a response is received from the tag in response to the command signal, determining that the tag is still operating, or if no response is received from the tag in response to the command signal, determining that the tag is not operating.

34. A controller station of claim 1, wherein the controller circuitry is configured with the receiver circuitry and the transmitter circuitry to transmit a control signal to the carrier wave emitter indicating that the carrier wave emitter should transmit a dedicated carrier wave to the tag to ensure the tag can respond by backscattering the reference signal.

35. A controller station of 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, an interface with the controller station being formed by the wireless access interface.

36. A controller station of claim 35, wherein one or more of the at least one carrier wave emitters are wireless communications devices which transmits the reference signal to the tag under the control of the infrastructure equipment.

37. A controller station of claim 35, wherein the reference signal transmitted by the wireless communications device as one of the carrier wave emitters is a synchronisation reference signal, SRS.

38. A controller station of claim 35, wherein the reference signal transmitted by the wireless communications device as one of the carrier wave emitters is a demodulation reference signal, DMRS.

39. A controller station of claim 36, wherein the wireless communications device is configured to transmit DMRS.

40. A controller station of claim 35, wherein the controller circuitry is configured with the receiver circuitry and the transmitter circuitry of infrastructure equipment forming the controller station of a wireless communications network to estimate a location of the tag by selecting a first set of wireless communications devices based on an estimated location of the tag, determining a distance of the tag from each of the wireless communications devices of the first set acting as carrier wave emitters by subtracting multipath profiles detected from reference signals transmitted by each of the wireless communications devices of the first set, and triangulating a position of the tag with respect to a known location of the controller station and of the wireless communications devices of the first set.

41. A controller station of claim 40, wherein the controller circuitry is configured with the receiver circuitry and the transmitter circuitry of infrastructure equipment forming the controller station of a wireless communications network to estimate a location of the tag by selecting a second set of wireless communications devices based on the estimated location of the tag from the wireless communications devices of the first set, the second set being in a better position to the tag than the first set, determining a difference in the time of flight of the reference signal from the wireless communications devices of the second set to the tag and to the controller station when the tag is in the reflective state, and from thewireless communications devices of the second set to the controller station when the tag is in the lower reflective state to determine a locus of possible locations of the tag with respect to each of the wireless communications devices of the second set acting as carrier wave emitters based on the additional times of flight determined from the reference signals transmitted by each of the wireless communications devices of the second set, and triangulating a position of the tag with respect to a known location of the controller station and of the wireless communications devices of the second set.

42. A controller station of claim 41, wherein the second set of wireless communications devices is in a better position relative to the tag by being closer than the first set.

43. A controller station of claim 42, wherein the second set of wireless communications devices is in a better position relative to the tag based on an angle to the tag compared to the first set.

44. A controller station of claims 41, wherein one or more of the wireless communications devices of the second set also forms part of the first set.

45. A controller station of claim 35, wherein the interface with the one or more carrier wave emitters is formed by a wireless access interface provided by the 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.

46. A radio tag, comprising an antenna, controller circuitry connected to the antenna, and backscattering circuitry connected to the antenna and to the controller circuitry, wherein the controller circuitry is configured to receive tag control information from a controller station for configuring an operation of the radio tag, and in response to the tag control information, to control the backscattering circuitry to be in a first state in which the backscattering circuitry in combination with the antenna are configured to more highly backscatter incident reference signals than a second state in which the backscattering circuitry and the antenna are configured to have a lower reflective state to backscatter signals than the first state.

47. A radio tag of claim 45, wherein controller circuitry is configured by the tag control information to control the state of the tag to backscatter the reference signal at different times in either of the first state or the second state, when the reference signal is transmitted by a carrier wave emitter.

48. A radio tag of claim 46, wherein controller circuitry is configured by the tag control information to control the state of the tag to be in the first state when the reference signal is transmitted at a first time by the at least one carrier wave emitter and to be in the second state when the reference signal is transmitted at a second time by the at least one carrier wave emitter.

49. A radio tag of claim 46, wherein controller circuitry is configured by the tag control information to control the state of the tag to remain in the same first or second backscatter reflection state for the plurality of different times when the reference signal is transmitted.

50. A radio tag of claim 46, wherein controller circuitry is configured by the tag control information to control the state of the tag to change from the first state to the second state at a modulation rate indicated by the tag control information.

51. A radio tag of claim 50, wherein the modulation rate identifies a first time period in which the tag should be in the first state and a second time period in which the tag should be in the second state, the modulation rate including the first and the second time periods, which are determined in accordance with a combination of a signal-to-noise ratio with which the reference signals are detected by the controller station, a coherence time of the radio channel through which the reference signals are detected and a detection period during which the tag is configured to change from the first state to the second state at the modulation rate, the detection period being determined in accordance with a number of tags from which a location is to be determined.

52. A radio tag of claim 50, wherein the tag control information includes a detection period during which the tag is configured to change from the first state to the second state at the modulation rate, and the tag control information includes an indication of a start of the detection period with respect to when the tag control information is received.

53. A radio tag of claim 50, wherein the tag control information configures the tag to change from the first state to the second state according to a sequence representing a cover code, from which a location of the tag can be determined contemporaneously with other tags.

54. A radio tag of claim 50, wherein the tag control information configures the tag to change from the first state to the second state at a modulation rate indicated by the tag control information, the modulation rate frequency shifting the backscattered signal reflected by the tag by switching between load impedances.

55. A radio tag of claim 54, wherein the frequency shift is different for each tag.

56. A carrier wave emitter operating in a communications system with a controller station and one or more tags, the carrier wave emitter comprising receiver circuitry configured to receive signals, transmitter circuitry configured to transmit signals, and controller circuitry configured to control the transmitter circuitry and the receiver circuitry, wherein the controller circuitry is configured with the transmitter circuitry and the receiver circuitry to receive control information for controlling the transmitter circuitry and in accordance with the control information, to transmit a reference signal at each of a plurality of different times for determining a location of a tag.

57. A method of controlling carrier wave emitters by a controller station in a communications system, the method comprisingtransmitting carrier wave emitter control information to a plurality of carrier wave emitters for controlling the carrier wave emitters to transmit a reference signal by each of the carrier wave emitters at each of a plurality of different times to a tag for determining its location, transmitting tag control information to the tag for controlling the state of the tag to backscatter the reference signal transmitted at each of the different times by each of the carrier wave emitters when the tag is in either a first state or a second state, and detecting the reference signal transmitted by each of the carrier wave emitters at the plurality of the different times, the reference signal being received according to a multipath profile derived from the received reference signal, wherein a state of the tag to backscatter the reference signal when transmitted by each of the carrier wave emitters at the different times changes from the first state to the second state, one of the first state and the second state being more highly reflective to backscatter incident signals than the other of the first state and the second state which is a lower reflective state to backscatter signals, the multipath detected in the more highly reflective state including paths from the reference signal backscattered from the tag, a difference between the detected multipath profiles for the first state and the second state being for use in estimating the location of the tag.

58. A method of claim 57, wherein the detecting the reference signal transmitted by each of the carrier wave emitters at the plurality of the different times comprises detecting the reference signal transmitted at each of the plurality of the different times by each of the plurality of carrier wave emitters, determining a different multipath profile from each reference signal received which is transmitted by each of the plurality of carrier wave emitters at each of the plurality of different times, and identifying a difference in the multipath profiles between when the tag is in a first state and when the tag is in a second state from the reference signals transmitted by each of the carrier wave emitters, the difference in the multipath profiles including a difference in a time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station when the tag is in the reflective state, and from the carrier wave emitter to the controller station when the tag is in the lower reflective state, the difference being for use in determining a distance of the tag from each of the plurality of carrier wave emitters for determining the location of the tag.

59. A method of claim 57, wherein the reference signal is transmitted by each of the plurality of carrier wave emitters periodically.

60. A method of claim 58, wherein the totality of different times for transmission of the reference signal is less than a coherence time of the radio channel via which the reference signal is received for use in deriving both multipath profiles.

61. A method of claim 57, wherein the identifying the difference in the multipath profiles between when the tag is in a first state and when the tag is in a second state from the reference signals transmitted by each of the carrier wave emitters comprises using a detected reference signal received on a direct path from each of the carrier wave emitters when the tag is in the first state and the second state as a datum,aligning and then subtracting the multipath profile detected when the tag is in the first state from the multipath profile detected when the tag is in the second state to identify the paths of the reference signal backscattered from the tag with reference to the datum, and determining the difference in the time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station when the tag is in the reflective state, and from the carrier wave emitter to the controller station when the tag is in the lower reflective state, the difference indicating an additional distance between the tag, one or more carrier wave emitters and the controller station in comparison to the distance from the carrier wave emitter to the controller station.

62. A method of claim 61 , comprising estimating a location of the tag by determining a path in the difference in the multipath profiles which is associated with a distance between the carrier wave emitter, the tag and the controller station, determining an additional time of flight of the reference signal from the carrier wave emitter to the tag and to the controller station from the determined path, determining a locus of possible locations of the tag with respect to each of a plurality of carrier wave emitters and the controller station, based on the additional times of flight determined from the reference signals transmitted by each of the carrier wave emitters at different times, , and triangulating a position of the tag with respect to a known location of the carrier wave emitters and the controller station.

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