EP4666405A1

EP4666405A1 - Devices, methods and system for target association in integrated sensing and communications systems

Info

Publication number: EP4666405A1
Application number: EP23710879.0A
Authority: EP
Inventors: Damiano BADINI; Christian Mazzucco; Marouane MIZMIZI; Dario TAGLIAFERRI; Umberto Spagnolini
Original assignee: Huawei Technologies Co Ltd; Politecnico di Milano
Current assignee: Huawei Technologies Co Ltd; Politecnico di Milano
Priority date: 2023-03-10
Filing date: 2023-03-10
Publication date: 2025-12-24
Also published as: CN121773564A; WO2024188413A1

Abstract

The present disclosure relates to target association for joint sensing and communications systems. A first device (as a user device) is configured to send its capability information to a second device (as a network device). The first device is configured to receive configuration information from the second device. The configuration information comprises an identification code and time information. The first device comprises a reconfigurable reflector. The reconfigurable reflector is configured to receive a sensing signal and perform time-varying reflections of the sensing signal during a period of time according to the time information. The time-varying reflections represent the identification code. In this way, a sensing unit for detecting the first device may not only locate the first device by the reflections of the sensing signal, but also determine the identification code based on the time-varying reflections. No additional signaling is needed to achieve the target association.

Description

DEVICES, METHODS AND SYSTEM FOR TARGET ASSOCIATION IN INTEGRATED SENSING AND COMMUNICATIONS SYSTEMS

TECHNICAL FIELD

The present disclosure generally relates to the field of communications technology. For instance, the present disclosure provides devices, methods, and a system for target association in integrated sensing and communications systems.

BACKGROUND

Sensing is becoming more and more important in next-generation wireless technologies such as sixth-generation (6G) communications systems. The recently emerged paradigm of integrated sensing and communication (ISAC) targets to fuse the two functionalities into a single one with both capabilities, for full frequency/time/space and hardware resource sharing. The inherent ISAC trade-off can be tuned to favor either communications or sensing. In the former case, the communications-centric ISAC design is suited to support beam and blockage management (e.g., reduction of the beam training time, proactive blockage prediction), resource allocation, etc. A vital aspect of the communications-centric ISAC design is a so-called target- to-user (T2U) association procedure (or simply, target association). The T2U association is to recognize, by the network side, which sensed targets are user equipments (UEs) that are connected over the communications interface of the ISAC system.

From the perspective of beam management, the importance of T2U association is clear, as the network side shall know the number and the position of the UEs to optimally handle communications (e.g., beamforming/beampattem design, resource allocation, etc.). Blockage prediction may also benefit from T2U association as beam blockage conditions apply to UEs, whereas other detected targets during sensing may be blockers. SUMMARY

The topic of T2U association in ISAC systems is seldom addressed in the field. A conventional approach may focus on sensing-aided vehicular communications. Radar and Global Positioning System (GPS) data are used to associate detected targets and vehicular UEs (VUEs). However, environmental factors often affect GPS communications, which reduces the accuracy and reliability of the T2U association in crowded scenarios. Moreover, exchanging GPS data needs a dedicated and always active low-rate uplink channel, which is cumbersome. Another conventional approach is to perform multi-vehicle tracking and ID association based on the Kullback-Leibler divergence between estimated and predicted vehicle states (range, velocity and angle). However, there is the issue of discriminating between collaborative (VUE) and non- collaborative targets, where the latter comprises both targets to be detected and clutter. For instance, urban environment is rich in clutter such as static targets and moving targets that are not VUEs. Moreover, vehicles appear as extended targets, thus any association method based on point-target assumption is limited to very low-resolution sensing systems.

In view of the above-mentioned problems and disadvantages, the present disclosure aims to tackle the T2U association issue in an ISAC system. An objective may be to provide a reliable and resource-saving method for the T2U association.

These and other objectives are achieved by this disclosure, for instance, as described in the independent claims. Advantageous implementations are further described in the dependent claims.

A first aspect of the present disclosure provides a first device comprising a reconfigurable reflector. The first device is configured to send capability information to a second device, and receive configuration information from the second device. The configuration information comprises an identification code and time information. The reconfigurable reflector is configured to receive a signal for sensing (or simply, a sensing signal) and perform time-varying reflections of the signal during a period of time according to the time information. The timevarying reflections of the signal represent the identification code.

Optionally, the reconfigurable reflector may be configured to perform time-varying reflections of the signal according to a binary representation of the identification code. For instance, the reconfigurable reflector may be configured to back-reflect the signal to an emitter emitting the signal for denoting a bit value of “1”. The configurable reflector may be configured not to back- reflect the signal to the emitter for denoting a bit value of “0”. It is noted that the notion of “back reflection” may be understood as a reflection configuration that allows maximizing reflected energy (e.g., a fraction of the impinging signal energy onto the reflection surface) in the same direction from which the signal insides on the reflector. As an example, for not back- reflecting the signal to the emitter, the reconfigurable reflector may be configured to perform a specular reflection or a diffusion reflection for the signal.

Alternatively, it is also possible that back-reflecting the signal may denote a bit value of “0”, while not back-reflecting the sensing signal may denote a bit value of “1”. This shall not be limited in the present disclosure.

By performing the time-varying reflections of the signal, the second device or sensing equipment may detect (or sense) the first device and, at the same time, determine the identification code that is represented by the time-varying reflections of the signal. In this way, the second device or the sensing equipment may associate the detected first device with the identification code. Moreover, the time-varying reflections of the signal are used for both sensing and identification. Therefore, the precision of T2U association can be increased.

Optionally, the identification code is not necessarily to be indicated by the configuration information from the second device. For instance, the first device may use any communications ID that is recognizable by the second device as the identification code. For instance, the communications ID may comprise any one or more of International Mobile Subscriber Identity (IMSI), Temporary Mobile Subscriber Identity (TMSI), International Mobile Equipment Identity (IMEI), Globally Unique Temporary Identity (GUTI), Subscription Permanent Identifier (SUPI), Subscription Concealed Identifier (SUCI), and the like. In this case, the configuration information may instead indicate which communications ID to be used for T2U association. Alternatively, a default communications ID (e.g., an IMSI) may be agreed upon between the first device and the second device to be used for T2U association, which is not necessarily indicated by the configuration information. Further, the associated first device may be aided by directional communications from the second device, in order to improve the stability of communications links in presence of beampointing, link-blockage and in high-frequency (e.g., millimeter wave (mmWave)) systems.

In an implementation form of the first aspect, before sending the capability information, the first device may be configured to receive a control message from the second device. The control message is for requesting (or polling) the capability information of the first device.

Alternatively, the first device may be configured to send the capability information through specific signaling without polling by the second device. For instance, the first device may be configured to promptly provide the capability information, e.g., during an attach procedure that is used to establish a communications link with the second device.

In a further implementation form of the first aspect, the capability information may comprise one or more of a type of the first device, a size of the first device, and the configurability information of the reconfigurable reflector. The configurability information is indicative of a quantity of reconfigurations supported by the reconfigurable reflector in a unit of time. Optionally, the configurability information may be further indicative of an accuracy of the reconfigurations.

Based on capability information, the second device may be aware of the information of the first device and the capability of the reconfigurable reflector of the first device. In this way, the second device may determine the configuration information based on the capability information. For instance, the identification code may be associated with the type and/or size of the first device. The time information may be set considering the reconfigurability information of the reconfigurable reflector and/or the accuracy of the reconfigurations. For instance, the reconfigurability information of the reconfigurable reflector may comprise the switching speed of the reconfigurable reflector (e.g., how fast the reconfigurable reflector can switch between different states in a unit of time).

In a further implementation form of the first aspect, the capability information may comprise a type of the first device. The type of the first device is associated with a size of the first device and/or configurability information of the reconfigurable reflector. The configurability information is indicative of a quantity of reconfigurations supported by the reconfigurable reflector in a unit of time. Optionally, the configurability information may be further indicative of an accuracy of the reconfigurations.

For instance, the capability information may be tabulated according to a pre-defined product list. The second device may be aware of the pre-defined product list or may be adapted to retrieve the pre-defined product list once being aware of the device type. Thus, the capability information may comprise the type of the first device. In this way, based on the type of the first device, the second device may be aware of the size of the first device and/or the configurability information of the reconfigurable reflector.

In a further implementation form of the first aspect, the identification code may be an orthogonal code. For instance, the identification code may be a Hadamard code.

In this way, interference between different first devices (e.g., to-be-detected and associated targets) may be mitigated.

In a further implementation form of the first aspect, the time information may be indicative of a starting time for starting the time-varying reflections and a duration for the reconfigurable reflector to hold each reflection status of the time-varying reflections.

Optionally, the starting time may be an absolute time point or a relative time point. The relative time point may be relative to a timestamp of the configuration information, or any other reference timestamp that can be agreed upon between the first device and the second device.

The duration for the reconfigurable reflector to hold each reflection status of the time- varying reflections may be simply referred to as a commutation interval. Each reflection status (i.e., back reflection or no back reflection) in a commutation interval may represent a corresponding bit value (e.g., bit “1” or bit “0”).

In a further implementation form of the first aspect, the reconfigurable reflector may comprise a reconfigurable intelligent surface (RIS) (or reconfigurable intelligent surfaces).

In a further implementation form of the first aspect, the signal for sensing may be an electromagnetic wave or a sound wave. In a further implementation form of the first aspect, a size of the reconfigurable reflector may be based on at least one or more of a frequency of the signal for sensing, a clutter density, and an accuracy requirement.

In a further implementation form of the first aspect, a reflectivity of the reconfigurable reflector may be at least 10 dB higher than a clutter reflectivity.

A second aspect of the present disclosure provides a second device. The second device is configured to receive capability information of a first device and send configuration information to the first device (in response to the capability information). The configuration information comprises an identification code for identifying the first device and time information, such that the first device performs time-varying reflections of a signal for sensing during a period of time according to the time information. The time-verying reflections of the signal for sensing represent the identification code.

It is noted that the first device comprises a reconfigurable reflector adapted to perform the timevarying reflections of the signal for sensing.

Optionally, the second device may be a network device for communications, such as a base station.

Optionally, the second device may further be capable of sensing. In this case, the second device may be further configured to send the signal for sensing to the first device, detect the timevarying reflections of the signal for sensing during the period of time according to the time information, and determine the identification code based on the detected time-varying reflections of the signal for sensing. Alternatively, the second device may be coupled with a network device for sensing (referred to as a sensing network device). In this case, the sensing network device is configured to send the signal for sensing to the first device, detect the timevarying reflections of the signal for sensing during the period of time according to the time information, and determine the identification code based on the detected time-varying reflections of the signal for sensing. The determined identification code may be notified by the sensing network device to the second device. In an implementation form of the second aspect, before receiving the capability information, the second device may be configured to send a control message to the first device. The control message is for requesting the capability information.

In a further implementation form of the second aspect, the second device may be further configured to, based on the capability information, obtain information on one or more of a type of the first device, a size of the first device, and configurability information of the reconfigurable reflector.

In a further implementation form of the second aspect, the identification code may be an orthogonal code. For instance, the identification code may be a Hadamard code.

In a further implementation form of the second aspect, the time information may be indicative of a starting time for the first device to start the time- varying reflections and a duration for the reconfigurable reflector to hold each reflection status of the time-varying reflections.

A third aspect of the present disclosure provides a system. The system comprises a communications unit and a sensing unit. The communications unit is configured to receive capability information of a first device and send configuration information to the first device. The configuration information comprises an identification code and time information. The system (the sensing unit or the communications unit) is configured to emit a signal for sensing. The sensing unit is configured to detect the first device based on an echo (or reflections) of the signal for sensing, and determine a corresponding identification code based on time-varying reflections of the signal received from the first device during a period of time according to the time information.

In this way, the detected first device can be associated with the determined identification code.

A fourth aspect of the present disclosure provides a method. The method is performed by a first device comprising a reconfigurable reflector. The method comprises the following steps: sending, by the first device, capability information to a second device, receiving, by the first device, configuration information from the second device, in which the configuration information comprises an identification code and time information; receiving, by the reconfigurable reflector, a signal for sensing; and performing, by the reconfigurable reflector, time-varying reflections of the signal representing the identification code during a period of time according to the time information.

In an implementation form of the fourth aspect, before sending the capability information, the method may further comprise receiving, by the first device, a control message from the second device. The control message may be for requesting the capability information.

In a further implementation form of the fourth aspect, the capability information may comprise one or more of a type of the first device, a size of the first device, and the configurability information of the reconfigurable reflector. The configurability information may be indicative of a quantity of reconfigurations supported by the reconfigurable reflector in a unit of time and optionally, an accuracy of the reconfigurations.

In a further implementation form of the fourth aspect, the capability information may comprise a type of the first device. The type of the first device may be associated with a size of the first device and/or configurability information of the reconfigurable reflector. The configurability information may be indicative of a quantity of reconfigurations supported by the reconfigurable reflector in a unit of time and optionally, an accuracy of the reconfigurations.

In a further implementation form of the fourth aspect, the identification code may be an orthogonal code.

In a further implementation form of the fourth aspect, the time information may be indicative of a starting time for starting the time- varying reflections and a duration for the reconfigurable reflector to hold each reflection status of the time-varying reflections.

In a further implementation form of the fourth aspect, the reconfigurable reflector may comprise a reconfigurable intelligent surface.

In a further implementation form of the fourth aspect, the signal for sensing may be an electromagnetic wave or a sound wave. In a further implementation form of the fourth aspect, a size of the reconfigurable reflector may be based on at least one or more of a frequency of the signal for sensing, a clutter density, and an accuracy requirement.

In a further implementation form of the fourth aspect, a reflectivity of the reconfigurable reflector may be at least 10 dB higher than a clutter reflectivity.

A fifth aspect of the present disclosure provides a method. The method comprises the following steps: receiving, by a second device, capability information of a first device; and sending, by the second device, configuration information to the first device, the configuration information comprises an identification code for identifying the first device and time information, such that the first device performs time-varying reflections of a signal for sensing during a period of time according to the time information, in which the time-verying reflections represent the identification code.

In an implementation form of the fifth aspect, before receiving the capability information, the method may further comprise sending, by the second device, a control message to the first device. The control message may be for requesting the capability information.

In a further implementation form of the fifth aspect, the method may further comprise obtaining, by the second device based on the capability information, information on one or more of a type of the first device, a size of the first device, and configurability information of the reconfigurable reflector.

In a further implementation form of the fifth aspect, the identification code may be an orthogonal code. For instance, the identification code may be a Hadamard code.

In a further implementation form of the fifth aspect, the time information may be indicative of a starting time for the first device to start the time-varying reflections and a duration for the reconfigurable reflector to hold each reflection status of the time-varying reflections. A sixth aspect of the present disclosure provides a computer program comprising a program code for performing the method according to the fourth aspect or any of its implementation forms.

A seventh aspect of the present disclosure provides a computer program comprising a program code for performing the method according to the fifth aspect or any of its implementation forms.

An eighth aspect of the present disclosure provides a non-transitory storage medium storing executable program code which, when executed by a processor (or a chipset), causes the method according to the fourth aspect or any of its implementation forms to be performed.

A ninth aspect of the present disclosure provides a non-transitory storage medium storing executable program code which, when executed by a processor (or a chipset), causes the method according to the fifth aspect or any of its implementation forms to be performed.

It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of the present disclosure, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The above-described aspects and implementation forms will be explained in the following description in relation to the enclosed drawings, in which

FIG. 1 shows an example scenario of the present disclosure; FIG. 2 shows an example of a first device and a second device according to the present disclosure;

FIG. 3 shows an example of time-varying reflections of a sensing signal according to the present disclosure;

FIG. 4 shows possible methods for not reflecting a sensing signal back to a sensing node according to the present disclosure;

FIG. 5 shows a diagram of a method according to the present disclosure;

FIG. 6 shows a diagram of a further method according to the present disclosure; and

FIG. 7 shows an example of RIS sizes with respect to different clutter densities.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows an example of a scenario of the present disclosure.

FIG. 1 depicts an ISAC system. The ISAC system comprises a base station (BS) equipped with at least two antenna arrays. At least one antenna array is used for sensing, and at least another antenna array is used for communications. Alternatively, a separate sensing system, such as radar, optical, acoustic, and any combination thereof may be co-located, or in the proximity of a communications system, such that an ISAC system is formed. In this disclosure, any network device capable of performing sensing may be referred to as a sensing node/unit. Any network device capable of performing communications may be referred to as a communications node/unit. A single network device may be capable of both sensing and communications. Alternatively, a communications node and a sensing node may jointly form an ISAC system.

The sensing node is adapted to sense the environment, such as to detect and/or create 2D/3D maps of objects. These objects may be referred to as targets. The environment may comprise a plurality of targets. The targets may comprise a target that is uninteresting to the ISAC system and interfere with observation of useful signals. The uninteresting target may be referred to as clutter. For instance, a mobile vehicle that is not (or not capable of) communicating with the base station may be seen as mobile clutter. A building may be seen as static clutter.

The problem of T2U association may be summarized that in an integrated sensing and communications system comprising at least two active communications devices (e.g., UEs), if sensing targets are labeled like {SI, S2, . . . }, and the communications devices are characterized by identification like {ID1, ID2, ... }, how to associated Sk with IDn such that sensing target Sk corresponds to communication device IDn. This may be complex due to the fact that the set of {Sk} is often much larger than the set of {IDn}.

A goal of T2U association is to identify UEs among all the observed targets during sensing. For instance, during sensing, the base station may observe several targets. Among these observed targets, there are UEs for the base station. The goal is to detect and identify these UEs. To this end, the UE according to this disclosure is equipped with a reconfigurable reflector, such as RIS. The RIS may be referred to a plurality of planar or conformal metasurfaces whose phase (and/or amplitude) can be dynamically configured to control the reflection properties of the metasurface itself. The metasurfaces (or referred to as reflecting elements) may be made of, e.g., sub-wavelength elements. According to this disclosure, the RIS may be phase-modulated and/or amplitude-modulated to encode UE ID into sensing echoes reflected by the RIS. In this disclosure, without loss of generality, the reconfigurable reflector and the RIS may be used interchangeably.

FIG. 2 shows an example of a first device 110 and a second device 120 according to this disclosure. For the sake of readability, in this disclosure, the first device 110 may be referred to as a UE, and the second device 120 may be referred to as a BS. In FIG. 2, a plurality of UEs (UE 1-5) is depicted for illustration purposes only. Any one of the UEs (UE 1-5) may correspond to the first device 110 of this disclosure.

The UE 110 comprises a reconfigurable reflector and is configured to send its capability information to the BS 120. Optionally, the capability information may comprise or be indicative of one or more of the following information: device type; device size; and configurability information of the reconfigurable reflector. The configurability information may also be referred to as device configurability limit, which may comprise information on different reconfigurations supported by the reconfigurable reflector in a unit of time (e.g., phase switching speed of RIS elements), and optionally, accuracy of the reconfigurations (e.g., phase quantization of the RIS element).

The capability information may be device-specific and can be provided to the BS 120 by either one of the following: requested by the BS 120 through specific signaling; sent by the UE 110 through specific signaling without BS pooling; forwarded by a neighboring BS during a handover procedure;

- tabulated in a pre-defined product list.

In the last case where the capability information is tabulated in the pre-defined product list, the BS 120 may only need to know the device type. Then, the BS 120 can be adapted to retrieve other capability information from the pre-defined product list in accordance with the device type.

In response to receiving the capability information, the BS 120 is configured to send configuration information to the UE 110. The configuration information may be determined based on sensing capabilities and based on capability information. Optionally, a plurality of UEs may be arranged into different clusters. As depicted in FIG. 1, UEs 1-3 are grouped into a cluster 130. Different clusters may be scheduled in a time division manner (as shown in FIG. 1), in a frequency division manner (not shown in FIG. 1), or based on location (not shown in FIG. 1). Identification codes are assigned by the BS 120 to each UE. The identification code is used to uniquely identify each UE with respect to the BS 120. When UEs are grouped into different clusters, it shall be sufficient that the identification code is unique in each cluster. It is also possible that the identification code is globally unique. This shall not be limited in the present disclosure.

The configuration information may be indicative or comprise one or more of the following information: identification code; and

- time information such as T2U procedure starting time and a commutation interval. The commutation interval may be referred to as a duration for the RIS to hold each reflection status during the T2U association procedure. Each reflection status may represent one bit, which is explained in the following in detail.

The communication of the capability information and the configuration information may be achieved through a communications interface.

For performing sensing, the BS 120 (or a sensing node) is configured to emit a sensing signal. The sensing signal may be any signal that can be used for sensing (objection detection). For instance, the sensing signal may be an electromagnetic wave, a sound wave, or a combination thereof. The electromagnetic wave may comprise one or more of a communications signal (e.g., with a carrier frequency of GHz or THz), a light signal (e.g., LiDAR signal, laser, etc.), a radar wave, and the like. For the purpose of sensing, the sensing signal can be received by the UE 110 and may be reflected by the UE 110.

In the T2U association procedure, during a period of time defined according to the time information comprised in the configuration information, the UE 110 is configured to perform time-varying reflections of the sensing signal using the RIS. The time-varying reflections represent the identification code.

For instance, as illustrated in FIG. 3, the identification code may be “1010”. The time information may indicate a starting time point tl and a commutation interval L. A T2U association procedure may be:

- From the time point tl to time point (t 1+L) : the RIS may be adapted to back reflect the sensing signal to the emitter (the BS 120 or the sensing node). The emitter thus detects an echo of the sensing signal during this period of time. This may represent bit “1”.

- From time point (tl+L) to time point (tl+2L): the RIS may be adapted not to reflect the sensing signal back to the emitter, such that the emitter does not detect an echo of the sensing signal during this period of time. This may represent bit “0”.

- From time point (tl+2L) to time point (tl+3L): the RIS may be adapted to back reflect the sensing signal to the emitter. This may represent bit “1”.

- From time point (tl+3L) to time point (tl+4L): the RIS may be adapted not to reflect the sensing signal back to the emitter. This may represent bit “0”.

In this way, during a period of time according to the time information (from time point tl to time point (tl+4L), the time-varying reflections of the sensing signal represent the identification code of “1010”. A similar fashion may apply to any other identification codes. It is noted that identification codes with all ones or all zeros shall be avoided, since they do not cause timevarying reflections of the sensing signal.

In this way, the emitter (or the base station) can correctly and reliably associate the detected targets with corresponding identifications. This is achieved during the sensing procedure. Therefore, there is no need to use a separate association procedure or using an additional channel.

Referring back to FIG. 2, five UEs are illustrated as an example and are grouped into two clusters: UEs 1-3 and UEs 4-5. In each cluster, the identification code assigned to each UE is unique. Alternatively, the identification code may be globally unique among all the UEs (not shown in FIG. 2). Optionally, the identification code may be an orthogonal code. For instance, the identification code may be a Hadamard code. Each cluster may share the same time information. For instance, UEs 1-3 may be configured to perform the time-varying reflections of the sensing signal representing a respective identification code during a common period of time.

A benefit of the present disclosure may be that the BS has the capability to estimate the position in space of each individual device that is communications-active. The “communications-active” may refer to a communications device that is connected to the network, or is in idle mode for the network but can be activated upon request. A further benefit is that radio access can be aided by a precise positioning for each active device (or user/UE). In an ISAC system (also known as joint communications and sensing (JCS), recognizing the position of an active UE can enable the BS to target a communications beam towards that active UE. The BS can also be able to avoid targeting the communications beam towards a clutter or a non-active UE, which can save energy. Hence, communications link stability can be improved in the presence of beam-point and link-blockage, especially in a high-frequency communications system such as a mmWave communications system. Optionally, one aspect of the present disclosure may provide a reconfigurable reflector, such as RIS. The reconfigurable reflector may be built or configured according to the present disclosure. The reconfigurable reflector may be attachable to a user device. The reconfigurable reflector is configured to perform time-varying reflections of a sensing signal emitted by a sensing node during a period of time. The time-varying reflections of the sensing signal represent an identification code identifying the user device. Time information defining the period of time for performing the time-varying reflections of the sensing signal may be obtained by the reconfigurable reflector from the user device. The time information may be pre-defined or may be configured to the user device by the network.

FIG. 4 shows possible methods for not reflecting a sensing signal back to a sensing node. A first possible method is to configure RIS of a UE with a constant phase across the reflecting elements of the RIS, such that a specular reflection is achieved. In this case, a sensing signal is not reflected back to the sensing node, but rather towards a different direction. A second possible method is to configure the RIS of the UE with random and uncorrelated phases across the reflecting elements of the RIS, such that a diffuse reflection is achieved. In this case, the sensing signal is omnidirectionally reflected, such that minimal energy can be reflected back towards the sensing node. In either case, the sensing node does not detect a reflection (or echo) of the sensing signal, which can denote a bit value of “0”. In contrast, for denoting a bit value of “1”, the reflecting elements of the RIS may be configured according to incidence angles of the sensing signal such that the sensing signal is back-reflected to the sensing node.

It is noted that FIG. 4 merely gives two possible examples for not reflecting the sensing signal back to the sensing node. However, other possible methods for not reflecting the sensing signal are not excluded. Any suitable method for configuring the RIS not to reflect an incoming signal back to its emitter can be used for denoting a bit value of “0”.

FIG. 5 shows a diagram of a method 500 according to the present disclosure. The method 500 is performed by a first device. The first device comprises a reconfigurable reflector.

The method 500 comprises the following steps: step 501: sending, by the first device, capability information to a second device; step 502: receiving, by the first device, configuration information from the second device, wherein the configuration information comprises an identification code and time information; step 503: receiving, by the reconfigurable reflector, a signal for sensing; and step 504: performing, by the reconfigurable reflector, time-varying reflections of the signal based on a binary representation of the identification code during a time duration based on the time information.

FIG. 6 shows a diagram of a further method 600 according to the present disclosure.

The method 600 comprises the following steps: step 601: receiving, by a second device, capability information of a first device; and step 602: sending, by the second device, configuration information to the first device, wherein the configuration information comprises an identification code for identifying the first device and time information.

The above two steps are performed by the second device as a communications node (or unit). When the second device is also capable of functioning as a sensing node, the method may further comprises the following steps: step 603: emitting, by the second device, a signal for sensing; step 604: detecting, by the second device, the first device based on an echo of the signal for sensing; step 605: determining, by the second device, a corresponding identification code based on time-varying reflections of the signal received from the first device during a period of time according to the time information; step 606: associating, by the second device, the detected first device with the corresponding identification code.

Optionally, the sensing node may be a separate node with respect to the second device. For instance, in a possible ISAC system architecture, a second device (e.g., a base station) is adapted to function as a communications node, and a separate sensing node may be deployed in the proximity of the communications node (such that any signal reflected back to the communications node can be captured by the sensing node). The communications node and the sensing node are coupled together and collaborate for joint sensing and communications. In this case, the above steps 604-605 is performed by the sensing node. Step 603 can be performed by the second device and/or by the sensing node.

It is noted that the steps of methods 500 and 600 may share the same functions and details from the perspective of FIGs. 1-4 described above. Therefore, the corresponding method implementations are not described in detail again at this point.

The present disclosure may be applied to any joint communications and sensing systems, such as but not limited to 5G, 5G-Advanced, 6G communications networks with sensing capability. Application scenarios of the present disclosure include but not limited to: Vehicle-to- Everything (V2X) networks, Internet-of-Things (loT) networks, massive Machine-Type Communications (rnMTC), etc.

Consider a downlink ISAC system depicted in FIG. 1. In the ISAC system, a base station is adapted for sensing the environment while serving K communication UEs, such as vehicle UEs. For simplicity, each UE is equipped with a single antenna receiving (Rx) unit and an M-element RIS. The environment comprises Q targets, which comprise L non-collaborative targets that do not have RIS and K UEs as collaborative targets. Q = K+L. By applying the present disclosure, the base station is capable of distinguishing the K collaborative targets from the L non- collaborative targets through sensing. Because the reflections of a sensing signal from the L non-collaborative targets do not vary with time.

To enforce RIS-aided T2U association, i.e., to pair K communication UEs with sensed K collaborative targets, each communications UE k is adapted to encode its unique ID represented by a binary sequence into the time-varying reflections of the RIS. The UE’s ID code encoding is implemented by letting the RIS vary its phase configuration as follows: if RIS of the fcth UE is back reflecting if RIS of the fcth UE is not back reflecting

(Eq. l) K is a positive integer larger than one, and & is a positive integer no greater than K. Defining with T as a fundamental unit of time of the ISAC system (e.g., either the radar pulse repetition interval or the symbol/slot time of a multicarrier communications waveform), each UE k is adapted to change its RIS configuration, switching from or vice versa, when there is a bitflip in the binary representation of its ID (from bit 1 to bit 0, or vice versa). Each UE is adapted to hold its RIS configuration for a commutation interval L. The commutation interval L may be equal to P*T. That is, the second device may indicate coefficient P to the first device (when T is pre-defined or commonly known by the first device and the second device). Generally, the second device may indicate the commutation interval L to the first device. The bit-length of the ID code is denoted as C. Thus, a total duration for a T2U association for a UE may be P=C*P*T. Parameters of P and C may affect the T2U association accuracy. Without loss of generality, an orthogonal code, such as a Hadamard code of length C>= K+l may be employed as the ID code. It is noted that codewords with all ones and all zeros may be avoided.

For achieving back reflection, the RIS of the k-th UE may be configured based on incidence angles of a sensing signal. The incidence angles of k-th UE may be denoted as (p_k = (0_fc, />_fc). For squared RIS with [M x [M reflecting elements, the phase at (//, v)-th element may be:

(Eq.2) where u and v are integers from 1 to [M. It is noted that Eq. 2 merely gives an example for achieving the back reflection. Any other suitable ways for achieving the back reflection are not excluded.

For achieving no back reflection, the RIS of each UE may be configured with a constant phase across the elements, such that a specular reflection is achieved. Alternatively, the elements of RIS of each UE may be configured with random and uncorrelated phases, such that a diffuse reflection is achieved. In these two cases, the energy reflected back to the sensing node is negligible. Thus, the sensing node cannot detect any echo of the sensing signal. When the first device is a mobile UE, such as a vehicle UE, mounting RIS on the vehicle may have a constraint, namely a limited space that restricts the size of the RIS accordingly. Thus, it may be desired to determine a sufficient size of the RIS, such that the back reflection can be detected by the sensing node. The size of the RIS may be based on, for example but not limited to, a sensing signal frequency, clutter density, and accuracy requirement. The clutter density may be understood as the number of clutter points per square meter. The accuracy requirement may be related to a probability of correct detection (PCD) of the K UEs from the environment. The PCD is associated with a probability of false alarm (PF A), such that PCD + PFA = 1. For meeting a high PCD value, the RIS may have a higher reflectivity than the clutter reflectivity. For instance, to ensure a PCD of at least 90% for a clutter density of 0.2 clutter points/m², the RIS may preferably have a reflectivity F_k of at least 10 dB higher than the clutter reflectivity. It is noted that the value of 10 dB is just given as an example/estimation. This value may vary with different conditions and IS AC system configurations. For instance, for a higher clutter density than 0.2 clutter points/m², 10 dB may not be enough to ensure a PCD with 90%.

FIG. 7 shows an example of RIS sizes with respect to different clutter densities, in view of different clutter reflectivity T_c and different accuracy requirements of PCD (denoted as P_Cd in FIG. 7). This result is obtained for a simulated ISAC system with the following configurations: frequency: 70GHz;

Tx power (BS): 20 dBm; bandwidth: 61 MHz; cell radius: 100 m; noise power level: -82 dBm; and number of UEs (K): 16.

In this simulation, the RIS is assumed to be a squire with side length of Ln_S. It is noted that the RIS according to the present may be in any shape. This result shows that RIS with area = 10 x 10 cm² (M « 94 x 94 reflecting elements) allows achieving a PCD > 99%. When the UE is a vehicle UE, this size is far below the size constraint, which for a commercial vehicle is in the level of square meters. It is noted that the size of 10 x 10 cm² is just given as a possible and optional value for the RIS in the simulated ISAC system. For various ISAC system configurations, the size of the RIS may be different. In summary, the present provides a user equipment equipped with a reconfigurable reflector. The reconfigurable reflector is adapted to perform time-varying reflections of a sensing signal. That is, the reconfigurable reflector is adapted to alternately reflect and not reflect the sensing signal back to a sensing node. The time-varying reflections represent an identification code associated with the user equipment. In this way, the sensing node observing the time-varying reflections can not only detect the user equipment but also know the identification code. Thus, the detected user equipment can be associated with the identification code. Therefore, the task of T2U association can be accomplished.

It is noted that the sensing node is not limited to a coherent sensor (e.g., radar, sonar) but can be any sensor capable of imaging the environment, e.g., camera, lidar, etc. For the operation of the T2U association, the UE is not required to either know the position of the sensing node, or its own position in space (local or absolute coordinates). Because the direction of the uplink communications link can be re-used to compute the optimal pointing for the reconfigurable reflector. However, if any additional information (such as the position of the sending node) is known, it could be used to simplify the T2U association. The UE is not required to be active during the T2U association procedure. That is, the UE does not need to transmit any communications signals in the uplink, toward the sensing node or the communications node. The identification code may be encoded in the time-varying passive parameters reconfiguration of the reconfigurable reflector. For instance, in the case of radio sensing, the reconfigurable reflector may be RIS. The phase and possibly amplitude of the RIS may be controlled to encode the identification code in the sensing image. The sensing image may be obtained by a standalone radar or by a communications node through echoes of the communications signal. Optionally, the type and length of the identification code may depend on UE capabilities, as well on the number of UEs. In case of RIS-aided T2U association for radar or ISAC systems, the RIS may be configured with a specific phase pattern (across the reflecting elements) in order to maximize the back-reflected power to the sensing node. If a UE equipped with the RIS is also equipped with a positioning system and is aware of the position in space of the sensing node, e.g., via GPS, it can use this information to rapidly steer the reflection beam towards the sensing node. If such position information is not available, the UE may configure the RIS to point in the same direction as a configurable antenna devoted to communications or as an incoming sensing signal. The present disclosure may be applied to a joint communications and sensing system that operates over the same or different portions of an EM spectrum, namely radio, THz, and optical.

The sensing node can generate a sensing image either by actively sensing the environment with an emitted signal or by using reflected signals from other sources (such as a communications signal from a communications node). The sensing node and the communications node may be separate nodes, or may be a same node. The sensing operation may comprise Line-Of-Sight (LOS) and/or Non-LOS (NLOS) scenarios. In LOS scenarios, UEs and any other targets (such as clutters) can be reached by the sensing and communication nodes through a direct optical path, which corresponds to the strongest path in terms of received power, both for sensing and communications. For sensing purposes, this allows directly associating a time/angle measurement to the position in space of the target. Differently, NLOS scenarios are characterized by the presence of a subset (or an entire set) of RIS-equipped UEs whose strongest path to/from the sensing node is not the direct one. For communications purposes, these UEs can be reached through secondary reflections that are found by periodic beam sweeping. For sensing purposes, the reconfigurable reflector described in this disclosure can still be used for distinguishing UEs in NLOS scenarios.

The first device and the second device in this disclosure may comprise processing circuitry (e.g., a chipset) configured to respectively perform, conduct or initiate the various operations described herein. The processing circuitry may comprise hardware and software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multipurpose processors. Optionally, the processing circuitry comprises one or more processors and a non-transitory memory connected to the one or more processors. The non-transitory memory may carry executable program code which, when executed by the one or more processors, causes the devices to perform, conduct or initiate the operations or methods described herein.

The present invention has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed invention, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

1. A first device (110) comprising a reconfigurable reflector, the first device (110) being configured to: send capability information to a second device (120), and receive configuration information from the second device (120), wherein the configuration information comprises an identification code and time information, wherein the reconfigurable reflector is configured to: receive a signal for sensing, and perform time-varying reflections of the signal representing the identification code during a period of time according to the time information.

2. The first device (110) according to claim 1, wherein before sending the capability information, the first device (110) is configured to receive a control message from the second device (120), wherein the control message is for requesting the capability information.

3. The first device (110) according to claim 1 or 2, wherein the capability information comprises one or more of a type of the first device (110), a size of the first device (110), and configurability information of the reconfigurable reflector, wherein the configurability information is indicative of a quantity of reconfigurations supported by the reconfigurable reflector in a unit of time and optionally, an accuracy of the reconfigurations.

4. The first device (110) according to any one of claims 1 or 2, wherein the capability information comprises a type of the first device (110), wherein the type of the first device (110) is associated with a size of the first device (110) and/or configurability information of the reconfigurable reflector, wherein the configurability information is indicative of a quantity of reconfigurations supported by the reconfigurable reflector in a unit of time and optionally, an accuracy of the reconfigurations.

5. The first device (110) according to any one of claims 1 to 4, wherein the identification code is an orthogonal code.

6. The first device (110) according to any one of claims 1 to 5, wherein the time information is indicative of a starting time for starting the time-varying reflections and a duration for the reconfigurable reflector to hold each reflection status of the time-varying reflections.

7. The first device (110) according to any one of claims 1 to 6, wherein the reconfigurable reflector comprises a reconfigurable intelligent surface.

8. The first device (110) according to any one of claims 1 to 7, wherein the signal for sensing is an electromagnetic wave or a sound wave.

9. The first device (110) according to any one of claims 1 to 8, wherein a size of the reconfigurable reflector is based on at least one or more of a frequency of the signal for sensing, a clutter density, and an accuracy requirement.

10. The first device (110) according to any one of claims 1 to 9, wherein a reflectivity of the reconfigurable reflector is at least 10 dB higher than a clutter reflectivity.

11. A second device (120) being configured to: receive capability information of a first device (110); and send configuration information to the first device (110), wherein the configuration information comprises an identification code for identifying the first device (110) and time information, such that the first device (110) performs time- varying reflections of a signal for sensing during a period of time according to the time information, wherein the time-verying reflections represents the identification code.

12. A system comprising a communications unit (120) and a sensing unit, wherein the communications unit (120) is configured to: receive capability information of a first device (110), and send configuration information to the first device (110), wherein the configuration information comprises an identification code and time information; the sensing unit or the communication unit (120) is configured to emit a signal for sensing; and the sensing unit is configured to: detect the first device (110) based on an echo of the signal for sensing, determine a corresponding identification code based on time-varying reflections of the signal received from the first device during a period of time according to the time information, and associate the detected first device (110) with the corresponding identification code.

13. A method (500) performed by a first device, wherein the first device comprises a reconfigurable reflector, and the method comprises: sending (501), by the first device, capability information to a second device, receiving (502), by the first device, configuration information from the second device, wherein the configuration information comprises an identification code and time information; receiving (503), by the reconfigurable reflector, a signal for sensing; performing (504), by the reconfigurable reflector, time-varying reflections of the signal based on a binary representation of the identification code during a time duration based on the time information.

14. A method (600) comprising: receiving (601), by a second device, capability information of a first device; and sending (602), by the second device, configuration information to the first device, wherein the configuration information comprises an identification code for identifying the first device and time information.

15. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to perform the method according to claim 13 or 14.