EP4385138A1

EP4385138A1 - Communication arrangement and method of operating a digitally controllable scatterer

Info

Publication number: EP4385138A1
Application number: EP21820205.9A
Authority: EP
Inventors: Mustapha Amara; Mohamed Kamoun; Maxime Guillaud; Melissa DUARTE GELVEZ
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2021-11-25
Filing date: 2021-11-25
Publication date: 2024-06-19
Also published as: WO2023093987A1

Abstract

A communication arrangement for communication over a plurality of frequency resources and a method for the operation thereof are disclosed. The communication arrangement includes a plurality of digitally controllable scatterers, DCSs, configured for frequency shifting electromagnetic radiation upon reflection thereon, assignment circuitry and channel estimation circuitry. The assignment circuitry is configured for assigning a respective frequency shift to each DCS of an active subset of the DCSs, and for assigning least one first frequency resource to one or more first communication nodes, CNs, for transmission of a respective pilot signal. The frequency shifts assigned to the DCSs of the active subset of DCSs are different from each other. The at least one first frequency resource and the frequency shifts are selected such that upon reflection of each pilot signal at each DCS of the active subset of DCSs, a reflected pilot signal having a frequency within a respective second frequency resource is obtained. The channel estimation circuitry is configured to obtain reception information from one or more second CNs and to perform a channel estimation on the basis thereof. The reception information is based on a reception of the reflected pilot signals by the one or more second CNs in the plurality of second frequency resources.

Description

COMMUNICATION ARRANGEMENT AND METHOD OF OPERATING A DIGITALLY

CONTROLLABLE SCATTERER

TECHNICAL FIELD

This application relates to the technical field of communication arrangements, more specifically to communication arrangements including digitally controllable scatterers, and to methods and computer programs for the operation thereof.

BACKGROUND

In the technical field of radio communication, a capacity of a radio channel between communication nodes (CNs) can be improved by providing multiple antennas in some or all of the communication nodes. Such techniques are denoted as Multiple-Input and Multiple-Output (MIMO) technologies. A CN can be, for example, a Base Station (BS) or a User Equipment (UE). MIMO technologies allow to exploit a spatial diversity of the communication channel of electromagnetic waves for improving channel capacity compared to Single-Input Single-Output (SISO) techniques wherein a single antenna is provided at each communication node.

For further improving radio communication, it has been proposed to move from solutions where channel diversity that occurs due to the propagation of electromagnetic waves in the environment of the communication nodes is exploited to solutions where the communication channel can be manipulated and adapted to specific needs. This can be done by introducing programmable surfaces called Digitally Controllable Scatterers (DCS), wherein a large number of reflective or scattering elements is provided on large surfaces. DCS can, for example, be implemented in the form of so-called Reflective Intelligent Surfaces (RIS), Intelligent Reflective Surfaces (IRS), or Large Intelligent Surfaces (LIS). The reflection phase shift of each element composing the surface can be controlled on its own. This enables shaping the communication channel by adapting to the requirements and the environment.

Fig. 1 schematically illustrates a DCS 100, a first CN 101, and a second CN102, which can be part of a set of CNs including further CNs which can have features similar to those of the first CN 101 and/or the second CN 102.

The DCS 100 includes a plurality of scattering elements 103, one of which is exemplarily denoted by reference numeral 104 in Fig. 1. The scattering elements 103 are adapted such that incident electromagnetic radiation, in particular electromagnetic radiation in a particular frequency range that is used for radio communication is reflected with a phase shift that can be electronically controlled. Examples of scattering elements include antennas connected to phase shifting circuitry and metamaterials. In Fig. 1, electromagnetic radiation emitted by the first CN 101 is schematically illustrated by dotted arrows. Electromagnetic radiation from the first CN 101 that is reflected by the DCS 100 towards the second CN 102 is schematically illustrated by dashed arrows. The reflection of electromagnetic radiation at the DCS 100 contributes to a communication channel from the first CN 101 to the second CN 102. The overall communication channel can be decomposed into two main components, which are the non- DCS channel 106, where electromagnetic radiation propagates from the first CN 101 to the second CN 102 without reflection at the DCS 100 and the DCS channel 105 where electromagnetic radiation is reflected at the DCS 100. For resource allocation, it is desirable to know the direct channel between the first CN 101 and the second CN 102 and the channel 105 via the DCS 105.

In an arrangement wherein a plurality of DCSs similar to the DCS 100 is provided, there can be a plurality of communication channels between the first CN 101 and the second CN 102. In addition to the non-DCS channel 106, there is a DCS channel similar to the DCS channel 105 via each of the DCSs. Furthermore, when communication between the first CN 101 and the second CN 102 is performed using a plurality of different frequencies, a separate determination of each of the communication channels may be required for each of the coherence bands.

In the prior art, techniques employing a subsequent activation of individual DCSs as well as techniques employing frequency modulations have been proposed. However, the techniques according to the state of the art are not efficient in time resource utilization for channel estimation and/or do not allow considering constraints on frequency and time resources available for channel estimation.

SUMMARY

The present disclosure provides communication arrangements and methods of communication over a plurality of frequency resources which help to address some or all of the above-mentioned issues.

According to a first aspect, a communication arrangement for communication over a plurality of frequency resources includes a plurality of digitally controllable scatterers, DCSs, assignment circuitry and channel estimation circuitry. The plurality of DCSs are configured for frequency shifting electromagnetic radiation upon reflection thereon. The assignment circuitry is configured for assigning a respective frequency shift to each DCS of an active subset of the plurality of DCSs, and for assigning at least one first frequency resource of the plurality of frequency resources to one or more first communication nodes, CNs, for transmission of a respective pilot signal. The frequency shifts assigned to the DCSs of the active subset of DCSs are different from each other. The plurality of frequency resources further includes a plurality of second frequency resources. The at least one first frequency resource and the frequency shifts assigned to the DCSs of the active subset of DCSs are selected such that upon reflection of each pilot signal at each DCS of the active subset of DCSs, a reflected pilot signal having a frequency within a respective second frequency resource of the plurality of second frequency resources is obtained. The channel estimation circuitry is configured to obtain first reception information from one or more second CNs. The first reception information is based on a reception of the reflected pilot signals by the one or more second CNs in the plurality of second frequency resources. The channel estimation circuitry is further configured to estimate, for at least one DCS of the active subset of the plurality of DCSs, at least one respective communication channel between at least one of the one or more first CNs and at least one of the one or more second CNs via the at least one DCS of the active subset of the plurality of DCSs on the basis of the first reception information.

In a possible implementation, the plurality of frequency resources includes one or more groups of frequency resources. Each group of frequency resources includes at least one first frequency resource and one or more second frequency resources. The frequency shifts assigned to the DCSs of the active subset of DCSs are selected such that, for each first frequency resource, upon reflection of each pilot signal transmitted by the one or more first CNs in the respective first frequency resource at each DCS of the active subset of DCSs, a reflected pilot signal having a frequency within the one or more second frequency resources of the same group of frequency resources is obtained.

In a possible implementation, each group of frequency resources includes two or more second frequency resources.

In a possible implementation, each group of frequency resources corresponds to a channel coherence band.

In a possible implementation, in each group of frequency resources, the at least one first frequency resource and the one or more second frequency resources of the respective group of frequency resources form a subset of the frequency resources of the respective group of frequency resources that are consecutive in frequency.

In a possible implementation, the channel estimation circuitry is configured to estimate, for each group of frequency resources, at least one respective communication channel between at least one of the one or more first CNs and at least one of the one or more second CNs via the at least one DCS of the active subset of the plurality of DCSs.

In a possible implementation, the one or more first CNs are a plurality of first CNs. Each group of frequency resources includes one first frequency resource that is assigned to each of the plurality of first CNs for transmission of the respective pilot signal. The pilot signals transmitted by the plurality of first CNs include at least one of orthogonal and semi-orthogonal signals within the one first frequency resource of each group of frequency resources.

In a possible implementation, the pilot signals transmitted by the plurality of first CNs are orthogonal in at least one of time and code. In a possible implementation, the one or more first CNs are a plurality of first CNs. Each group of frequency resources includes a plurality of first frequency resources. In each group of frequency resources, a different first frequency resource of the plurality of first frequency resources of the respective group is assigned to each of the plurality of first CNs.

In a possible implementation, the active subset of the plurality of DCSs includes all of the plurality of DCSs.

In a possible implementation, the plurality of DCSs are further configured for switching between an active state and an inactive state. Each DCS of the plurality of DCSs that is in the inactive state provides a weaker reflection of the pilot signals from the one or more first CNs to the one or more second CNs than when it is in the active state. The communication arrangement further includes circuitry for switching, in each of a plurality of time intervals, a different subset of the plurality of DCSs into the active state and for switching the other DCSs of the plurality of DCSs into the inactive state. In each of the plurality of time intervals, the active subset of the DCSs is formed by the subset of the plurality of DCSs that are in the active state in the respective time interval.

In a possible implementation, each of the plurality of DCSs is in the active state in at least one of the plurality of time intervals.

In a possible implementation, the assignment unit is configured to assign, for each of the plurality of time intervals, a respective frequency shift to each DCS of the subset of the DCSs that are in the active state in the respective time interval. The channel estimation circuitry is configured to estimate, for each of the plurality of time intervals, a respective communication channel from at least one of the one or more first CNs to at least one of the one or more second CNs via at least one DCS of the subset of the DCSs that are in the active state in the respective time interval on the basis of the first reception information that is obtained for the respective time interval.

In a possible implementation, at least a part of the plurality of DCSs includes a plurality of scattering elements. At least a part of the plurality of scattering elements is adapted such that a reflection phase shift thereof is electronically controllable. The at least a part of the plurality of DCSs further includes circuitry for controlling the reflection phase shifts of said at least a part of the plurality of scattering elements such that in the active state of the respective DCS and in the inactive state of the respective DCS, the pilot signals are scattered in specific directions. In the inactive state, less energy is scattered towards the second CNs.

In a possible implementation, at least a part of the plurality of DCSs includes a plurality of scattering elements. At least a part of the plurality of scattering elements is adapted such that a reflection amplitude thereof is electronically controllable. The at least a part of the plurality of DCSs further includes circuitry for controlling the reflection amplitude of said at least a part of the plurality of scattering elements such that in the active state of the respective DCS, the reflection amplitude of said at least a part of the plurality of scattering elements is greater than in the inactive state.

In a possible implementation, the plurality of frequency resources further includes at least one third frequency resource that is a different frequency resource than the at least one first frequency resource and the plurality of second frequency resources. The assignment circuitry is configured to assign the at least one third frequency resource to the one or more first CNs and the one or more second CNs for data transmission.

In a possible implementation, the plurality of frequency resources further includes a plurality of fourth frequency resources that are different frequency resources than the first, second and third frequency resources. The fourth frequency resources are selected such that, for each of the at least one third frequency resource, a data transmission signal having a frequency in the respective third frequency resource is frequency shifted into a respective one of the plurality of fourth frequency resources upon reflection at each DCS of the active subset of the plurality of DCSs.

In a possible implementation, the plurality of frequency resources includes one or more groups of frequency resources. Each group of frequency resources corresponds to a channel coherence band. Each group of frequency resources includes at least one third frequency resource and at least one fourth frequency resource.

In a possible implementation, at least a part of the plurality of DCSs includes a plurality of scattering elements, at least a part of the plurality of scattering elements being adapted such that a reflection phase shift thereof is electronically controllable. The at least a part of the plurality of DCSs further includes circuitry for applying a temporal variation of the reflection phase shift of the at least a part of the plurality of scattering elements. A frequency of the temporal variation corresponds to the frequency shift assigned to the respective DCS.

In a possible implementation, the assignment circuitry is further configured to assign a respective scattering pattern to each DCS of the active subset of the plurality of DCSs.

In a possible implementation, the assignment circuitry is provided at one of the one or more first CNs. The one of the one or more first CNs is configured to transmit information representative of the respective frequency shift assigned to each DCS of the active subset of the plurality of DCSs and to transmit information representative of the at least one first frequency resource to the one or more second CNs.

In a possible implementation, the assignment circuitry is further configured to transmit the information representative of the at least one first frequency resource to the plurality of DCS. In a possible implementation, the one of the one or more first CNs is a base station.

In a possible implementation, the channel estimation circuitry is provided at at least one of the one or more second CNs.

In a possible implementation, the at least one of the one or more second CNs is configured to transmit channel state information that is based on the estimation performed by the channel estimation circuitry to the one of the one or more first CNs.

In a possible implementation, the assignment circuitry and the channel estimation circuitry are provided at one of the one or more second CNs. The one of the one or more second CNs are configured to transmit information representative of the respective frequency shift assigned to each DCS of the active subset of the plurality of DCSs and information representative of the at least one first frequency resource to the one or more first CNs.

In a possible implementation, the one of the one or more second CNs is a base station.

In a possible implementation, the plurality of frequency resources are evenly spaced in frequency. At least a part of the frequency shifts assigned to the active subset of the plurality of DCSs is an integer multiple of a frequency spacing between adjacent frequency resources of the plurality of frequency resources.

In a possible implementation, the frequency shifts assigned to the active subset of the plurality of DCSs are upward shifts to a higher frequency.

In a possible implementation, the plurality of second frequency resources are different frequency resources than the at least one first frequency resource. The channel estimation circuitry is further configured to obtain second reception information from the one or more second CNs. The second reception information is based on a reception of the pilot signals by the one or more second CNs in the at least one first frequency resource. The channel estimation circuitry is further configured to estimate at least one non-DCS communication channel between at least one of the one or more first CNs and at least one of the one or more second CNs on the basis of the second reception information.

According to a second aspect, in a method of communication over a plurality of frequency resources, a respective frequency shift is assigned to each digitally controllable scatterer, DCS, of an active subset of a plurality of DCSs. At least one first frequency resource of the plurality of frequency resources is assigned to one or more first communication nodes, CNs, for transmission of a respective pilot signal. The frequency shifts assigned to the DCSs of the active subset of DCSs are different from each other. The plurality of frequency resources further includes a plurality of second frequency resources. The at least one first frequency resource and the frequency shifts assigned to the DCSs of the active subset of DCSs are selected such that upon reflection of each pilot signal at each DCS of the active subset of DCSs with the frequency shift assigned to the respective DCS, a reflected pilot signal having a frequency within a respective second frequency resource of the plurality of second frequency resources is obtained. A respective pilot signal is transmitted in the at least one first frequency resource by each of the one or more first CNs. At each of one or more second CNs, the reflected pilot signals are received in the plurality of second frequency resources. For at least one DCS of the active subset of the plurality of DCSs, at least one respective communication channel between at least one of the one or more first CNs and at least one of the one or more second CNs via the at least one DCS of the active subset of the plurality of DCSs is estimated on the basis of the reflected pilot signals received at the one or more second CNs.

BRIEF DESCRIPTION OF DRAWINGS

In the following, embodiments will be described with reference to the drawings, wherein:

Fig. 1 shows communication channels in an arrangement including a DCS and two CNs;

Fig. 2 shows a communication arrangement;

Fig. 3 shows a CN;

Fig. 4 shows a DCS;

Figs. 5a to 5d show configurations of scattering surfaces of DCSs;

Fig. 6 shows communication channels in the communication arrangement of Fig. 2;

Fig. 7 shows components of communication channels that are present in a communication arrangement that utilizes multiple frequency resources and multiple DCSs;

Figs. 8a to 8c show a flow diagram illustrating a method of communication;

Fig. 9 shows a scattering pattern of an inactive DCS;

Fig. 10 shows an assignment of frequency resources;

Fig. 11 shows another assignment of frequency resources;

Fig. 12 shows a further assignment of frequency resources;

Fig. 13 shows exchanges of signals in a method of communication; and

Fig. 14 shows exchanges of signals in another method of communication. DESCRIPTION OF EMBODIMENTS

The present disclosure provides embodiments of communication arrangements and methods of communication wherein digitally controlled scatterers (DCSs) are used. Constraints on available time and frequency resources for channel estimation are taken into account in order to define which DCSs are active during each channel estimation time slot and to assign, at each channel estimation time slot, a frequency shift to each active DCS.

In embodiments disclosed herein, the frequency shifting capabilities of DCSs through modulation techniques are used in order to facilitate the estimation of the non-DCS channel and the DCS channels between a base station (BS) and multiple user equipments (UEs) for multiple DCSs at the same time. The selection of the frequency shift applied by each DCS takes into account the constraints on available time and frequency resources for channel estimation such that with the T time slots and W frequency resources available one can estimate the non-DCS channel and the DCS channels for each DCS and for a set of frequency resources. In embodiments, data can be transmitted during the resource allocation process in frequency resources that are not used for channel estimation during the allocated T time slots.

Fig. 2 shows a schematic view of a communication arrangement 200 according to an embodiment. The communication arrangement 200 includes a plurality of DCSs 201, 202, 203 and a plurality of communication nodes (CNs) 204, 205, 206, 207. As shown in Fig. 2, the CN 204 can be a BS and the CNs 205-207 can be UEs or repeaters. A communication channel between BS 204 and the UEs 205-207 is in part via the DCSs 201, 202, 203. The wireless signals between the BS 204 and UEs 205-207 propagate via non-DCS paths that are illustrated by dotted line arrows and via DCS paths that are illustrated by solid line arrows.

The present disclosure is not limited to embodiments wherein one BS and a plurality of CNs are provided, as shown in Fig. 2. For example, the plurality of CNs 204-207 can include more than one BS, or all the CNs can be UEs. It can also include repeaters, lABs and other network components. Generally, there can be K UEs and D DCSs. In addition to one or more BSs and one or more UEs, the plurality of CNs can include one or more access points (APs).

Fig. 3 shows a schematic block diagram of a CN 300 according to an embodiment. The CN 300 can be a UE such as, for example, one of the CNs 205-207 shown in Fig. 2, or a BS such as, for example the BS 204 shown in Fig. 2. The CN 300 can include antennas 301, 302. The number of antennas can be one or two, as shown in Fig. 3. In other embodiments, a greater number of antennas can be provided. Providing two or more antennas can allow performing communication in accordance with MIMO technologies. In further embodiments, for example in embodiments wherein the CN 300 is a UE, a single antenna can be provided. However, UEs having more than one antenna can also be used. The CN 300 can include transmiter circuitry 303 and receiver circuitry 304, which are connected to the antennas 301, 302, and can be used for transmiting and/or receiving pilot signals and data signals for transmiting and/or receiving various types of information. Additionally, the CN 201 can include computation circuitry 305, which can include a processor and memory. The computation circuitry can be used for carrying out various algorithms, as will be described below. The computation circuitry 305 can be used for performing various types of data processing at the CN when methods of communication using the CN are carried out as described in detail below, so that the computation circuitry can be configured so as to include circuitry for various purposes. In particular, the computation circuitry 305 can include assignment circuitry 306 for assigning frequency resources for the transmission and reception of pilot signals and for assigning frequency shifts to the DCSs 201, 202, 203, as well as channel estimation circuitry 307 for performing channel estimations. Moreover, in embodiments, the computation circuitry 305 can include circuitry 308 for controlling the switching of the DCSs 201, 202, 203 between an active and an inactive state. The circuitry 308 for controlling the switching of the DCSs 201, 202, 203 between an active and an inactive state can be configured for sending signals to the DCSs 201, 202, 203 which instruct the receiving DCS to switch to the active or inactive state, respectively. The active and inactive state of a DCS as will be explained in more detail below. Circuitry for configuring phase shifts of the scatering elements of the DCSs can also be provided in the CN.

Fig. 4 schematically illustrates a DCS 400 which can be implemented in the form of an Intelligent Reflective Surface (IRS) or Reflective Intelligent Surface (RIS). In embodiments, some or all of the DCSs 201, 202, 203 of the communication arrangement 200 can have features corresponding to those of the DCS 400. The DCS 400 includes a scatering surface 401 and a controller 402. The scatering surface 401 includes a plurality of scatering elements 407, one of which is exemplarily denoted by reference numeral 408. The plurality of scatering elements 407 can be adapted such that reflection phase shifts of the scatering elements of the plurality of scatering elements 407 (which will be denoted as “scatering elements 407” in the following) for electromagnetic radiation are electronically controllable. In some embodiments, each of the scatering elements 407 can include an antenna and phase shifting circuitry. The phase shift provided by the phase shifting circuitry can be electronically controlled so as to provide the reflection phase shift of the scatering element. In other embodiments, the scatering elements can include meta-material elements configured to provide a reflection phase shift for electromagnetic radiation in the predetermined frequency range that can be electronically controlled. By controlling the reflection phase shifts of the scatering elements 407, directions into which electromagnetic radiation impinging on the scatering surface 401 of the DCS is scatered can be controlled.

Additionally, by applying a temporal variation of the reflection phase shifts of the scatering elements 407, a frequency shift of electromagnetic radiation reflected at the scatering surface 401 of the DCS 400 can be obtained. The obtained frequency shift corresponds to the frequency of the temporal variation. Thus, upon reflection of impinging electromagnetic radiation at the scattering surface 401 of the DCS 400, reflected electromagnetic radiation having a higher or lower frequency than the electromagnetic radiation impinging on the scattering surface 401 of the DCS 400 can be obtained. Additionally and/or alternatively, the scattering elements 407 can be adapted such that reflection amplitudes of the scattering elements 407 for electromagnetic radiation are electronically controllable, as will be explained in more detail below.

The DCS 400 can further include a controller 402. The controller 402 can include interface circuitry 403 for connecting the controller 403 to the scattering elements 407 of the DCS 400, and computation circuitry 404, which can include a processor and a memory so that the computation circuitry 404 can be configured as circuitry for various purposes. In particular, the computation circuitry 404 can include circuitry 405 for controlling the reflection phase shifts of the scattering elements 407, circuitry 406 for applying a temporal variation of the reflection phase shifts of the scattering elements 407 and/or circuitry 409 for controlling the reflection amplitudes of the scattering elements 407.

The present disclosure is not limited to embodiments wherein each of the DCSs 201, 202, 203 has a scattering surface 401 that is substantially planar, as shown in Fig. 4. In other embodiments, some or all of the DCSs can include scattering surfaces having a non-planar configuration, as will be described in the following with reference to Figs. 5a, 5b and 5c.

Fig. 5a schematically illustrates a scattering surface 501a, which can be used as an alternative to the scattering surface 401 of the DCS 400 shown in Fig. 4. The scattering surface 501a includes a plurality of scattering elements 407, one of which is exemplarily denoted by reference numeral 408. The scattering surface 501a has a non-planar configuration, wherein a front side of the scattering surface 501a is convex. The front side of the scattering surface 501a is the side on which, in the operation of the DCS 400, the electromagnetic radiation reflected at the scattering surface 501a impinges. For example, in embodiments, the scattering surface 501a can be mounted on a wall of a building. In such embodiments, the front side of the scattering surface 501a is the side of the scattering surface that is averted from the wall.

Fig. 5b schematically illustrates a scattering surface 501b, which can be used as another alternative to the scattering surface 401 of the DCS 400 shown in Fig. 4. The scattering surface 501b includes a plurality of scattering elements 407, one of which is exemplarily denoted by reference numeral 408. The scattering surface 501b has a non-planar configuration, wherein the front side of the scattering surface 501b is concave.

Fig. 5c schematically illustrates a scattering surface 501c, which can be used as a further alternative to the scattering surface 401 of the DCS 400 shown in Fig. 4. The scattering surface 501c includes a plurality of scattering elements 407, one of which is exemplarily denoted by reference numeral 408. The scattering surface 501c has a non-planar configuration, wherein the front side of the scattering surface 501c includes portions having a different curvature. For example, the front side of the scattering surface 501c can include convex portions, concave portions and/or saddle-shaped portions.

Moreover, the present disclosure is not limited to embodiments wherein the scattering surface of the DCS 400 is provided as a single piece. Fig. 5d schematically illustrates a scattering surface 50 Id, which can be used as a further alternative to the scattering surface 401 of the DCS 400 shown in Fig. 4. The scattering surface 501d includes a plurality of DCS blocks 502, 503, 504, 505, which can be distributed. Thus, the scattering surface 501d is not provided as a single piece. The scattering surface 501d includes a plurality of scattering elements, wherein each of the DCS blocks 502-505 includes a subset of the scattering elements. The DCS blocks 502-505 can have a non-planar configuration, as shown in Fig. 5d. In other implementations, some or all of the DCS blocks 502-505 can be planar. The scattering elements of the DCS blocks 502-505 can be operated in a coordinated manner, so that the scattering surface 501d is provided as a virtual DCS scattering surface.

Referring to Fig. 2 again, the controllable reflection phase shifts of the scattering elements of each of the DCSs 201, 202, 203 provide a way to modify the scattering pattern of the respective DCS, and hence to modify the communication channel between the BS 204 and the UEs 205-207 in order to improve the downlink and uplink communication. Knowing the contribution of each DCS 201, 202, 203 to the overall communication channel between the BS 204 and each UE 205-207 can be important for designing the communication algorithms that exploit the presence of DCSs 201-203 for improved downlink and uplink performance. The achieved improvement depends on the available channel state information (CSI).

Embodiments described herein provide solutions for estimating the contribution of each DCS 201, 202, 203 to the overall communication channel between BS 204 and UEs 205-207. This can be a challenging task, in particular when the scattering elements of the DCSs 201-203 are not connected to radio frequency (RF) chains. In this case, the DCSs 201-203 cannot estimate propagation conditions and cannot transmit pilot signals either. This means that the contribution of each DCS 201, 202, 203 to the overall communication channel can only be measured either at the BS 204 or at the UEs 205-207 via signals transmitted only either by the BS 204 or the UEs 205-207. This complicates the task of characterizing the overall communication channel via each of the DCSs 201, 202, 203.

In embodiments described herein, a plurality of frequency resources can be available for communication between a BS such as the BS 204 and a plurality of the UEs 205-207. Assume a set A_LL ⁼ ■■■ <fw} °f cardinality W contains a list of all the W frequency resources available for communication between the BS 204 and the UEs 205-207. A model for the overall communication channel between the BS 204 and the fc-th one of the UEs 205-207 at frequency resource is the following: Equation (1) where the first term H_{o k}y^ represents a non-DCS channel that is formed by the aggregated contribution of non-DCS paths between the BS 204 and the fc-th one of the UEs 205-207 at frequency and the second term is the summation of the communication channels between the BS and the /c -th UE over the D DCSs 201, 202, 203 at frequency The contribution of the d-th DCS is represented as H_{DCSd k} ^and D is the number of DCSs (in the example of Fig. 2, D = 3).

The terms of Equation (1) are schematically illustrated in Fig. 6. Fig. 6 shows the BS 204, the DCSs 201, 202, 203 and the UE 206 which are also shown in Fig. 2. The DCS 201 has been denoted by the index d = 1, the DCS 202 has been denoted by the index d = 2, and the DCS 203 has been denoted by the index d = D. The UE 206 has been denoted by the index k = 1. The terms of the overall communication channel for UE 206 are shown next to the arrows that illustrate the DCS channels and the non-DCS channel for UE 206. Corresponding terms of the overall communication channel are present for each of the other UEs 205, 207 shown in Fig. 2.

The model in Equation (1) above is, for example, representative of an orthogonal frequency -division multiplexing (OFDM) communication system with W frequencies fi_,f₂, ■■■ fw where, for each UE, the delay spread due to all non-DCS and DCS paths is less than the cyclic prefix duration. Each of the frequencies fi_,f₂, - ,fw can ^sP^{an one or} more subcarriers.

The present disclosure provides techniques for estimating the non-DCS channel H_{o k} ^ and the D DCS h l H d {1,2 ... , D between a BS (for example, BS 204 shown in Fig. 2) and UE k, for (for example, UEs 205-207 shown in Fig. 2) and each frequency resource w}- Techniques disclosed herein can be applied both for uplink (where the UE acts as a transmitter for pilot signals and thus the channels for propagation from UE to BS ^Ho,fc = and H_DCSdik = H_UEk^_DCSd^_BS are estimated) and downlink (where the BS acts as a transmitter for the pilot signals and thus the channels for propagation from BS to UE H_{o k} = H_BS->UEk and H_{DCSd k} = H_Bs->Dcs_d->uE_k ^are estimated) channel estimation. Hence, for a UE k and frequency resource a total of D + 1 channel matrices can be estimated. For a BS with M antennas and a UE k with N_k antennas, each of the channel matrices H_0;fey and has MN_k elements. Gathering channel matrix estimates for the non-DCS contribution and each DCS contribution for the entire W frequency resources means an estimation of a total of W(D + 1) matrices for each UE. Fig. 7 schematically illustrates the channel matrices that are to be estimated per UE. For each of the W frequency resources fi_,f₂, ■■■ there is one non-DCS channel matrix H_{o k}^ and there are D channel matrices H_DCS ... , H_{DCS fe} - for the communication channels via the D DCSs. Thus, for each UE, a total of D + 1 channel estimates per frequency resource is to be estimated. Having knowledge of the non-DCS channel and the D DCS channels H_{DCSd k} ^for each UE and frequency resource provides useful information for resource allocation. For example, this information can be used by the scheduler to know which DCS is a good choice to serve a UE k by comparing the channel quality via each DCS using the computed H_DCSdik^.

In embodiments disclosed herein, the required time and estimation procedure for a set of D DCSs is compressed within T timeslots. Techniques disclosed herein exploit the capability of DCSs to modulate an incident signal and provide a frequency shifted version of it as a scattered signal. The frequency shift induced by the DCS can be controlled such that the shift of two DCSs are different. Thus, a method of realizing multiple channel estimations for an active subset D' of the DCSs, D' c {1, . . , D}, with the same pilot signal sent by the BS in a given timeslot can be provided.

Given a target number of time slots T for channel estimation, at least D' = |D'| DCS can be activated in each of the time slots {t_x, t₂, ... , t_T , Each DCS in the active state provides a stronger reflection of pilot signals from one or more CNs to one or more other CNs than when it is in an inactive state. Thus, the reflection of the pilot signals from a DCS in the inactive state is weaker than the reflection of the pilot signals from the DCS in the active state. In particular, active DCSs can have a contribution to the overall communication channel between BS and UEs that is measurable and inactive DCSs can have a negligible or at least relatively small contribution to the propagation between BS and UEs. In embodiments, the choice of D' active DCSs per time slot can be such that at the end of the last time slot T each of the D DCSs has been activated at least once. One possible configuration can be uniform and thus D' = D/T.

Given an input set of frequency resources T_ALL = {f ,f₂, ... ,fw}- a different frequency shift value A _d can be assigned to each active DCS d in time slot t_T such that if an impinging wave has a frequency component at frequency resource that belongs to T_ALL then the reflected wave from the DCS due to this frequency component is centered at a frequency resource + A _d that also belongs to the set of available frequency resources _ALL. Although the impinging wave at the DCS and the reflected wave from the DCS are at different frequencies, this constraint on the assigned frequency shift has the advantage of guaranteeing that the reflected wave is also utilizing one of the available frequency resources. Thus, by receiving the reflected waves, reception information can be obtained.

The frequency resources assigned for pilot signal transmission and reception can be chosen such that if is used for pilot signal transmission and DCS d is active with a frequency shift A _d, then the frequency resource is used only for pilot signal reception. Thus, it can be ensured that the signal received a contains only the contribution due to DCS d. This has the advantage that an estimate of the contribution of DCS d to the communication channel can be obtained by observing only the received signal at frequency The signals received at time slots {ti, t₂, ■■■ , t_T] provide reception information that can be used to compute an estimate of the non-DCS channels and DCS channels for the D DCSs, K UEs and W frequency resources.

Figs. 8a, 8b and 8c show a flow diagram illustrating a CSI acquisition procedure. As shown in Fig. 8a, at 801, input data is obtained. The input data can include a list of K UEs denoted by index k, a list of D DCSs denoted by index d. a list of T time slots t_T denoted by index T and a list of W frequency resources denoted denoted by index a>. For example, when performing the CSI acquisition procedure for the communication arrangement described above with reference to Fig. 2, the input data can include a list of the K = 3 UEs 205, 206, 207, a list of the D = 3 DCSs 201, 202, 203, as well as lists of time slots and frequency resources.

Then, an allocation step 802 of performing resource allocation for the channel estimation is performed. The allocated resources include frequency resources assigned to one or more CNs for transmission and reception of pilot signals as well as frequency shifts assigned to the DCSs. Thereafter, as shown in Fig. 8b, a transmission step 803 of performing over the air transmission for channel estimation is performed. Then, as shown in Fig. 8c, an estimation step 804 of channel estimation is performed, and output is provided at 805. The output can include respective non-DCS channels H_{o k}y^for each of the UEs that are denoted by index k and each of the frequency resources and communication channels H_Dcs_d,fc,/_(/)via each of the DCSs that are denoted by index d for each of the UEs k and frequency resources

The allocation step 802 will be described in more detail with reference to Fig. 8a in the following. At substep 806, an active subset D'(t_T) c {1, . . , D} of the D DCSs is identified for each time slot t_T, T = 1, 2, ... , T. The choice of active DCSs per time slot can be based on different inputs. For example, for a given configuration of the BS (adopted beamforming) at instant t_T one can activate a subset D'(t_T) of DCSs that are in the BS beams. As another example, one can simply choose 'D'(t_T) randomly. The choice of D'(t_T) can be selected such that each of the D DCSs is activated at least once during the T time slots.

At substep 807, each active DCS d in time slot t_T is assigned a different frequency shift A/_d(t_T). Thus, it can be avoided that contributions from multiple DCSs are superimposed in time and frequency which might occur if simultaneously active DCS are not assigned different frequency shifts and which might hinder the channel estimation process. For introducing a different frequency shift A/_d(t_T) for each DCS d E T)'(t_T'), the modulation capabilities of the DCS can be exploited, as will be described in more detail below. This way, for a pilot signal transmitted at the channel perceived from an active DCS d at time slot t_T can be measured at frequency This enables separation between the various scattered pilot signals and consequently facilitates estimation of the DCS channels.

At substep 808, a set T_P-rx(t_T) of first frequency resources for transmission of pilot signals by CNs such as, for example, the BS and/or the UEs is defined. At substep 809, a set T_PKX(t_T) of second frequency resources wherein pilot signals are received is constructed for each time slot. The received pilot signals can include pilot signals received via non-DCS channels and pilot signals reflected at the DCSs. The reflected pilot signals can be received by CNs such as, for example, the BS and/or the UEs. In particular, for obtaining CSI information for downlink, pilot signal transmission can be performed by the BS and the reception of the reflected pilot signals can be performed by some or all of the UEs. For obtaining CSI information for uplink, pilot signal transmission can be performed by the UEs, and the reflected pilot signals can be received by the BS.

At substep 810, it can be verified if a constraint relating to the measurability of the reflected pilot signals is fulfilled. In particular, in order to be able to measure the pilot signals reflected by an active DCS d, it can be helpful to ensure that if G TpTxtir) then + A/_d(t_T) G d^J _PliX(t_T). Also, in order to be able to measure the non-DCS channel, it can be helpful to ensure that if G J^: _PTX(t_T) then G FpR_X(tr). The sets Fprx(tr) ^ancl FpRx(tr) ^ancl the chosen A/_d(t_T) are selected such that all propagation happens within the given set of frequency resources F_ALL . Hence it can be ensured that F_PTX (t_T ) G F_ALL and Tp-rx(t_T) ^e FALL- If the constraint is not fulfilled, substeps 807, 808, 809 can be iterated for providing modified sets iFp_rx(t_T) and F_PRX(t_T).

At substep 811, it can be determined if sets F_PTX (t_T ) and F_PRX (t_T) have been provided for all time slots t_T. If no, substeps 807-810 are performed for the resource assignment for the next timeslot. If yes, the process continues with the transmission step 803, which will be described with reference to Fig. 8b in the following.

In the transmission step 803, substep 812 of transmitting pilot signals and substep 813 of receiving reflected pilot signals are performed in each of the T time slots t_T. At substep 812, pilot signals are transmitted on the frequencies G J^: _P-l-x(t_T) for the set of frequencies FpT_X(tr) that ^was determined for the respective time interval at substep 808. At substep 813, the pilot signals are received at the frequencies G F_PRXQt_T). The transmission of pilot signals can be performed by CNs such as, for example, the BS and/or the UEs. In a downlink scenario, pilot signal transmission can be performed by the BS and the reception of the pilot signals can be performed by some or all of the UEs. In an uplink scenario, pilot signal transmission can be performed by the UEs, and the pilot signals can be received by the BS. The received pilot signals include reflected pilot signals which are obtained upon reflection of the pilot signals at the DCSs of the active subset of DCSs, as well as pilot signals that have propagated from the transmitting CN to the receiving CN through non-DCS channels without reflection at a DCS. Based on the received pilot signals, reception information can be provided which includes data about the received pilot signals that are required for performing channel estimation.

After performing substeps 812 and 813, at substep 814, it is determined if the index T of the current timeslot is equal to the total number T of timeslots, i.e., if substeps 812, 813 have been performed for all timeslots. If no, substeps 812, 813 are performed for the next timeslot. It yes, the process continues with the estimation step, which will be described with reference to Fig. 8c in the following.

In the estimation step, substep 815 of estimating the non-DCS channel matrices for each frequency ) in the set of frequencies for transmission of pilot signals and substep 816 of estimating a part of the DCS channel matrices are performed on the basis of the reception information provided on the basis of the pilot signals received at substep 813. In particular, at substep 815, the signal received at each time slot t_T and frequency G Fprx(tr) is used to estimate the non-DCS channel. For UE k this channel is denoted as H_o (t_T). At substep 816, The signal received at each time slot t_T and frequency + A/_d(t_T) is used to estimate the channel from all DCS d G D'(t_T) due to transmission at G FpTx(tr) ^aiqd reception at For UE k this channel is denoted as

HDCs_d,fc,(/_w,/_w+A/_d(tj) (fr)- The channel estimation can be performed using known techniques for channel estimation such as least squares estimation or minimum mean square error (MMSE) estimation.

After performing substeps 815 and 816, at substep 817, it is determined if the index T of the current timeslot is equal to the total number T of timeslots, i.e., if substeps 815, 816 have been performed for all timeslots. If no, substeps 815, 816 are performed for the next timeslot. It yes, substep 818 is performed, wherein the non-DCS channel and the DCS channel ^are computed for each of the frequency resources for each of the DCSs and for each of the CNs that have been used for receiving pilot signals (in the case of a downlink scenario) or for sending pilot signals (in the case of an uplink scenario). Examples of how the computation can be performed will be described below in the context of the description of Algorithm 1 and the algorithms according to Embodiments 3, 4 and 5.

In some embodiments, the frequency resources not used for channel estimation can optionally be allocated for data transmission. This can be done by taking into account the frequency shift introduced by the DCSs for resource allocation. A detailed description of the proposed algorithm and taking into account the option of data transmission is provided in Algorithm 1, which will be described in the following.

Algorithm 1:

Similar to step 801 of the CSI acquisition procedure described above with reference to Fig. 8, Algorithm

1 includes an obtaining of input data. The input data include the following data: A list of K UEs {U E_x , UE₂, ... , UE_K } involved in the channel estimation procedure. These are the UEs for which an estimate of the non-DCS and DCS channels between BS and UE is required.

• A list of D DCS {DCS^ DCS₂, ... , DCS_D} involved in the channel estimation procedure. These are the DCSs that create the DCS channels the estimation procedure will estimate. This input list may contain, or not, all the DCSs present in the environment. One DCS may also be split into two DCS by splitting the scattering elements into two non-overlapping subsets, hence each subset is identified as a different DCS.

• A list of T time slots t₂, ... , t_T] available for the channel estimation procedure. A suitable choice is to define T time slots that are within the coherence time of the channel. This ensures that the channel variations over time are negligible during the estimation process.

• A list of W frequency resources T_ALL = {f_r,f₂, ... ,f_w] for which non-DCS and DCS channel estimates are required.

When performing Algorithm 1, the following constraint for the number T of time slots, the number W of frequency resources and the number D of DCSs should be taken into account:

• Constraint 0 (CO): The total time-frequency resources available for channel estimation (TIV) should be greater than the number of channels to estimate D + 1 per UE. Thus

TW > D + 1 Equation (2) should hold for full estimation. This constraint allows the activation of each of the D DCS at least once during the T time slots.

Algorithm 1 includes an allocation step similar to the allocation step 802, a transmission step similar to the transmission step 803 and an estimation step similar to the estimation step 804 of the CSI acquisition procedure described above with reference to Fig. 8. These steps will be detailed in the following.

Allocation step: Resource allocation for channel estimation for t_T = t , t₂, ... , t_T , i.e. for each time slot t_T in input set t₂, , ... , t_r):

• Define a set iFp_rx(t_T) G F_ALL of first frequency resources for pilot signal transmission and define a set & FALL of second frequency resources for pilot signal reception. A frequency resource can be both in set F_PTX (t_T ) and in set F_PRX (t_T ) . Define which DCSs are active and which are inactive, wherein an inactive DCS has a negligible contribution or at least a relatively small contribution to the propagation between the BS and the UEs. This is done as follows: o Define an active subset D'(t_T) c {1, . . , D} of the DCSs. o Give priority for activation to the DCSs that have not yet been set as active. In the first time slot fy there has been no active DCS assigned yet by the algorithm. Hence, for the first time slot, all DCSs can have the same priority for activation.

• For each active DCS, i.e. each DCS d G T)'(t_T'), assign a frequency shift to be applied at time slot t_T: o The applied frequency shifts can be upshifting such that or downshifting such that To obtain an upshift of A/, we set = hf and to obtain a downshift of A/, we set = —bf. The DCS configuration in order to achieve upshifting or downshifting is explained in Embodiment 1. o OPTIONALLY : Besides a frequency shifting, each DCS d can also be assigned a scattering pattern that for example focuses energy in a specified direction, for example towards a given UE or subset of UEs. In Embodiment 1, it will be specified how to set the phase of the scattering elements in order to achieve simultaneous frequency shifting and beam focusing.

• The frequency shifts per time slot assigned to active DCSs and the sets of frequency resources per time slot Tfy-_x(t_T ) and defined for pilot signal transmission and reception should satisfy the following set of constraints:

Constraint 1 (Cl). Equation (3)

This means that if a frequency resource belongs to Tp_TX(t_x\ then the frequency shifts assigned to active DCSs at time t_T must be such that belongs to . Furthermore if a frequency resource belongs to Tfy-_x(t_T ) then this frequency must also belong to F_PRX since this resource will be used for estimation of the non-DCS channel.

• OPTIONALLY : At this point, some frequency resources in the input set may be left unused, since there may be some resources which are used neither for pilot signal transmission nor for pilot signal reception. The algorithm may leave these frequencies as unused or use them for data transmission. The data transmission shall take into account the previously defined sets of frequency resources for pilot signals F_PTX (t_T ) and F_PRX (t_T ) ^and the DCS shifts A/d(t_T). The assignment of data transmission to a frequency resource that is not used for pilot signals, i.e. f_w £ {TpTx(t_T) ^u ^PRX^T ) } is done as follows: o Define a set of third frequency resources for data transmission and define a set

^DRX^T^ °f fourth frequency resources for data reception. A frequency resource can be both in set ?_DTX (t_T ) and set T_{D RX} (t_T ) . o The sets of frequency resources per time slot Furx^-)' and T’_D;i>_x(t_T ) defined for data transmission and reception should satisfy the following constraints:

Constraint 2 (C2). Afy (t_T) G Equation (4)

Constraint 2 specifies that, if a frequency resource belongs to T ^xit^ , then the data transmitted at that frequency will be received at frequency via DCS d.

Hence, frequency resource shall be assigned for data reception.

Constraint 3 (C3). Equation (5)

Constraint 3 specifies that a frequency resource used for pilot signal transmission cannot be used for data transmission. end for

Transmission step: Over the air transmission for channel estimation

• Inform each of the DCSs in the input set {DCS^ DCS₂, ... , DCS₀} of the selected active or inactive state for each DCS for each time slot in input set {t_x, t₂, , ... , t_T}. The selected frequency shift for each active DCS in each time slot is also informed.

If needed, inform list of input UEs {UE₁, UE₂, ... , UE_K} of the selected pilot signal and data frequency resource assignments J^: _PTxCt_T'),J^: _PRXQt_T'),J^: _DTXQt_T'),J^: _DRXQt_T ') and shifts Afy(t_T) for each time slot in input set {t₁, t₂, , ... , t_T}. Notice when these sets do not vary one may not need to inform again the UEs every time.

• Perform over the air transmission during the T time slots and via the W frequency resources by using the time and frequency resource allocation scheme defined in the allocation step.

Estimation step: Channel estimation

• The resource allocation designed in the allocation step and the transmission in the transmission step allows to estimate at each time slot t_T and UE k : o The non DCS channel H_{o fe} at time slot t_T , denoted as H_{o fe} (t_T ), for each frequency resource o The DCS channel H_DCSd,_fe;(r(urx,_/(ufix) at time slot t_T , denoted as H_DCSd,_fe;(r(urx,_/(ufix) (t_T ), which corresponds to the channel for UE k observed at frequency resource f_MRX due to DCS d which applies a frequency shift A/_d(t_T)that shifts the signal impinging at the DCS arriving at frequency f_MTX & F_TRX(t_T) to a frequency f_MRX = f_MTX + A/_d(t_T) such that fwRx ^G F ‘ pRxtt-c} ^as P^er the design in the allocation step.

The estimations can be performed using known techniques for channel estimation such as least squares estimation or minimum mean square error (MMSE) estimation.

• The estimates of H₀,_fe,_/(U(t_T) and labeled as and respectively, computed based on the signals received at time slots t_T, T = 1,2, ... , T, are used in order to compute the required non-DCS channel H_{o k}^ and DCS channel H_{DCSd fe} estimates for all D DCS, all W frequency resources and all K UEs.

• It is also a possibility that not all for all D DCS, all W frequency resources and all K UEs are required. For example, just knowledge of and may suffice for subsequent communication after the channel estimation phase. Consequently, this step computes only the required information that is needed for subsequent communication and the information of what information is required may be an input to the algorithm.

Optional data processing step: Process received data

If some of the frequency resources were assigned in the allocation step for data communication then the data processing step consists in processing the received data using the channel estimates obtained in the estimation step. In the following, further embodiments will be described.

Embodiment 1: Frequency shifting using a DCS

This embodiment provides an example explaining how frequency shifts can be achieved via the control of the scattering properties of a DCS. In the following, it will be described how a DCS d such as, for example, any of the DCSs 201, 202, 203 described above with reference to Fig. 2 having features corresponding to those of the DCS 400 described above with reference to Fig. 4 can be used for producing a reflected wave at frequency + f_&d given an impinging wave at frequency wherein f_&d is a frequency shift that is created upon reflection at the DCS. For convenience of description, in the following, reference will be made to the DCS 400. As detailed above, the DCS 400 includes a plurality of scattering elements 407. In the following, the number of the scattering elements 407 will be denoted as S’.

The impinging wave can be, for example, a pilot signal transmitted by a CN such as, for example, the BS 204 or one of the UEs 205-207 described above with reference to Fig. 2. Thus, upon reflection of the pilot signal having the frequency at the DCS 400, which will be denoted by the index d. a reflected pilot signal having a frequency + f_&d can be obtained, wherein the frequency of the reflected pilot signal differs from the frequency of the pilot signal transmitted by the CN by the frequency shift

The CN can have features corresponding to those of the CN 300 described above with reference to Fig. 3. Consider a transmitter (TX) antenna such as, for example, one of the antennas 301, 302 of the CN 300 transmitting at carrier frequency a complex baseband signal x (t ) having average unit magnitude while using total power P^TX. The TX pass band signal is given by Equation (6) and the received signal at a receiver (RX) antenna of another CN due to the scattered contribution from only one scattering element s of DCS d can be modeled as where c is the speed of light, r^_CSd is the distance traveled by the wave from the TX to the RX, <t>_D ^scs_d( )

RX is the time varying phase shift applied by DCS d scattering element s, P_DCs_d i^s the received signal power which is a function of the TX power, P^TX . wavelength = c/f_M , antenna gain, radar cross section of the scattering element s and angles of arrival and departure.

The time varying phase <t>Dcs_d(t) °f the scattering element s can be provided by controlling the scattering element s by means of the controller 402 of the DCS. Similarly, the controller 402 of the DCS 400 can be employed for controlling the other scattering elements 407 of the DCS 400, so that a time varying phase shift can be provided for each of the scattering elements 407 of the DCS 400.

Controlling the term <j>D_Cs_d(t) ^can be used to generate a phase shift by choosing Equation (8) which consists of a constant term c/>f_)CSd and a time variable term 2n:f_&dt. Using Equation (8) in Equation (7) we can rewrite the received signal as

Equation (9)

By aggregating the contribution from the S surface elements 407 of the DCS 400, we obtain the received signal from the entire scattering surface 401 of the DCS 400 that is denoted by index d:

Equation (10)

This corresponds to a passband signal centered at frequency + f_& Hence, the DCS 400 has effectively shifted the frequency by the frequency shift and the reflected signal is centered at + /_Ad while the impinging signal was centered at

The fixed phase shift per unit cell <p_D ^s _Cs_d ^can also be controlled for example to obtain beam focusing. Hence, the choice of <t>Dcs_d(t) can be used for example for simultaneous beam focusing and frequency shifting.

The frequency shift described in Equation (8) results in an upshift of the impinging signal. In other embodiments, a downshift of the impinging signal can be provided. For this purpose, the time varying phase of the scattering elements can be chosen as Equation (11)

Embodiment 2: Setting a DCS into the inactive mode As mentioned above, in embodiments disclosed herein, DCSs can be switched between an active state and an inactive state. Each DCS that is in the inactive state provides a weaker reflection of the pilot signals from one or more transmitting CNs to the one or more receiving CNs than when it is in the active state. In particular, the reflection of the pilot signals obtained from an inactive DCS can be so weak that it has a negligible contribution to the overall communication channel. In this embodiment we explain two ways to set a DCS as inactive.

In the first implementation, a DCS such as, for example, the DCS 400 described above with reference to Fig. 4 is provided, whose scattering elements 407 are adapted such that their reflection amplitudes for electromagnetic radiation are electronically controllable. The scattering elements 407 can be switched between a configuration wherein the reflection amplitude of the scattering elements 407 is relatively high, so that a relatively large fraction of electromagnetic radiation impinging on the scattering surface 401 of the DCS 400 is reflected and a configuration wherein the reflection amplitude of the scattering elements 407 is relatively low, so that only a small amount of electromagnetic radiation is reflected at the scattering surface 401 of the DCS 400. In the configuration wherein the reflection amplitude of the scattering elements 407 is relatively low, the electromagnetic radiation can be transmitted through the scattering surface 401 of the DCS 400. The configuration wherein the reflection amplitude of the scattering elements 407 is relatively low can be provided, for example, by detuning a resonance frequency of the scattering elements 407 with the frequency of the incident pilot signals. In some implementations, this can be done by means of one or more actuators for mechanically moving components of the antennas of the scattering elements 407 and/or by switching inductive and/or capacitive circuit elements of the scattering elements 407. Thus, an impact of the DCS on the propagation of electromagnetic radiation can be completely removed or at least substantially reduced so that its contribution to the channel is negligible.

In the second implementation, in the inactive state of the DCS 400, the reflection phase shifts of the scattering elements 407 of the DCS 400 are controlled such that, upon reflection of electromagnetic radiation at the DCS 400, the radiated energy is spread in all directions, hence minimal with respect to the energy received from an active DCS. An example of such a radiation pattern is shown in Fig. 9.

Embodiment 3: Channel estimation in one time slot with UEs sharing frequency resources for pilot signals

This is an embodiment for the case of channel estimation in one time slot (T = 1), wherein the UEs share frequency resources for pilot signals. Without loss of generality and for sake of simplicity to explain this embodiment, we further define and clarify the following notation and assumptions:

There are W = 4(D + 1) frequency resources ■■■ ,fw ■ The spacing between adjacent frequency resources is the same and equal to y hence fi₊₁ — fi = y. Thus, the frequency resources are evenly spaced in frequency.

• Notice constraint CO in Equation (2) is satisfied since WT = 4(D + 1) > D + 1.

• Pilot signals for different UEs share the same frequency. For the downlink this is a straightforward scenario. For the uplink this means that UEs transmit pilot signals in shared frequency resources and utilize orthogonal or semi-orthogonal pilot signals within the same frequency resource, for example pilot signals that are orthogonal in at least one of time and code.

Allocation step: Resource allocation for channel estimation for t_T = t_r, i.e. for the single time slot T = 1:

• Divide the frequency resources into G groups, labeled as GI> G2' > --- Gc- where each group represents a set of neighboring frequency resources. Each group can correspond to a channel coherence band. For simplicity, to explain this embodiment we choose the cardinality of each group, denoted as \G_g | for group fig, to be the same for all groups and equal to |5_a | = IV/2 = 2(D + 1)/T. Given the total W = 4(D + 1) frequency resources, the single time slot T = 1 and the group size |5_a | = IV/2 = 2 (D + 1), one can construct a total of G = 2 groups, labeled as 51'52- by assigning to each group the same number of frequency resources equal to IV/2 and creating groups 5iand Q₂ as ordered sets with elements 5i = {/1-/2- ■■■ >fw/2 } ^aiqd Gt ⁼ {fw/2 + l ’fw /2+2 > ■■■ > fw] where fi < fj for i < j.

The set FpTxCh ') of first frequency resources for pilot signal transmission is chosen as the lowest frequency per group, thus

F prxCti ) ⁼ {fi'fw/2+1 }■ Equation (12)

If we further define J 'f- e set of frequency resources for pilot signal transmission used at time t_T group Q_g, then we have that

? prxtfi iGi) ⁼ {fi} and ? prxtfi 1G2) ⁼ {fw/2+1 }• Equation (13)

This assignment means that the lowest frequency per group is used for pilot signal transmission as shown in Fig. 10.

The set F_PRX (tf) of second frequency resources for pilot signal reception is chosen as the lowest D + 1 frequencies per group, thus Equation (14)

If we further define F ‘ pR the set of frequency resources for pilot signal reception used at time for group Q_g. then we have that

Equation (15)

This assignment means that the lowest D + 1 frequencies per group are used for pilot signal reception as shown in Fig. 10. Accordingly, the frequencies per group that are used for pilot signal transmission and pilot signal reception are consecutive in frequency.

• Activate D/T DCS during the single time slot t_x. Since T = 1, all D DCSs are activated during the single time slot t_1; so the active subset D'(tr) = {1,2, ... , D }. Thus, the active subset of the DCSs includes all of the D DCSs. For each DCS d = 1,2, ... , D, a frequency shift is assigned that upshifts the impinging signal by d frequency resources. Thus, A/_d(t_T) = dy. wherin y is the spacing between adjacent frequency resources and is assumed in this embodiment to be the same between all adjacent frequency resources. Consequently, for a pilot signal transmitted at frequency resource the channel from DCS d can be measured at frequency resource f^+a- This is shown in Fig. 10, where we can for example observe that for a pilot signal transmitted at f_r, the contribution from DCS 1 is measured at /₂ and so on, such that the contribution from DCS D is measured at /₀₊₁.

• Notice constraint Cl in Equation (3) is satisfied since + dy G FpRxCh ) and f_w/_{2 +2} + dy G ? PRX^I )

• OPTIONALLY : At this point half of the frequency resources are unused during time slot so one option is to use those frequency resources for data transmission as follows:

Define as the set of frequency resources for data transmission used at time in group Q_g. For one time slot and two groups we define Equation (16)

The groups are also shown in Fig. 10.

Define F_DRX (t_x, Q_g ) as the set of frequency resources that are used for data reception at time in group Q_g. For one time slot and two groups, we define Equation (17)

These groups are also shown in Fig. 10.

The set of third resources for data transmission at time slot is Equation (18) and the set of fourth resources for data reception at time slot U is

Equation (19)

The assignments defined by Equation (12), Equation (14), Equation (18) and Equation (19) satisfy constraint C2 in Equation (4) and constraint C3 in Equation (5). end for

The resource allocation for channel estimation and optional data transmission defined in the allocation step is communicated to involved devices and used for over the air transmission as described in the following transmission step.

Transmission step: Over the air transmission for channel estimation

Perform signal exchange to inform the involved entities of the resource allocation described in the allocation step. Possible embodiments of signaling exchanges for downlink and uplink pilot signal exchange are provided later in Embodiments 6 and 7.

Perform over the air transmission during the single time slot and via the W frequency resources by using the time and frequency resource allocation scheme defined in the allocation step. o In a scenario of downlink pilot signal transmission, the resource allocation defined in this embodiment and illustrated in Fig. 10 is used as follows: The BS transmits pilot signals on

G FpTxCh ) and ^each UE receives pilot signals on G FpRxtfi )■ The BS uses G ^DTxCfi ) t° transmit data. The data can be for all UEs or for a single UE. The concerned UE or UEs receive this data o In a scenario of uplink pilot signal transmission, the resource allocation defined in this embodiment and illustrated in Fig. 10 will be used as follows: Each UE transmits pilot signals on G T’prxCU ) and different UEs use orthogonal pilot signals. The BS receives pilot signals on G Fp_Rx(ti )• One or several UEs transmit data on G Forx^i ) and the BS receives this data

The signals received on second frequency resources G F_PRX(t₁ ') after the over the air transmission in the transmission step and using the resource allocation in the allocation step are used in the estimation step for channel estimation as follows.

Estimation step: Channel estimation

• For each UE k, estimate the non-DCS channel H_{o k}y^ for all W frequency resources A-/2- fw as follows Equation (20)

Recall frequencies and Av/2+1 ^were used f°^r pilot signal transmission and reception, hence the non-DCS channels H₀,k,A (U) and H₀,fc,/_w/2+1 (U) for UE k can be directly estimated from the received signal at frequencies and Av/2+1 at the single time slot t_x, as shown in Fig. 10, and their respective estimates are denoted as H_{o kji} (t₁) and Ho,fc,/_w/2+1 (ti)- These estimates can be determined on the basis of the transmitted and received pilot signals using known techniques for channel estimation such as least-squares estimation and MMSE estimation and are used as inputs to function I_o which uses this information to estimate the non-DCS channel for all frequency resources Thus, function (t₁)) is such that it combines the knowledge of HQ.^JU) and Ho.k/w/z+i (U) via interpolation or extrapolation or some other means in order to output an estimate of H_o denoted as H_o An example of function I_Oj is the following:

The assignments described by Equation (21) mean that for all frequencies belonging to group , the non-DCS channel estimate H_{o fe} is set to be equal to H_{o fe} (t_x) and for all frequencies belonging to group £₂ the non-DCS channel estimate H_{o k}y^ is set to be equal to Ho,fc,/w/₂+i (U)- Groups g_r and £₂ ^{are as} defined in the allocation step of this embodiment and also shown in Fig. 10. The function described by Equation (21) is particularly accurate for the case where each group corresponds to a channel coherence band. A coherence band is a range of frequency resources whose frequency separation is less than the coherence bandwidth. The coherence bandwidth is the frequency interval over which the channel can be assumed highly correlated. The channel matrices for all frequency resources within a coherence band are thus highly correlated and can be approximated to be the same. If the coherence bandwidth and the resulting coherence bands are known, then this information can be input to the algorithm and the groups defined in the allocation step can be designed so as to match the input coherence bands.

For each UE k, estimate the DCS channel H_{DCSd fe} (t_x) for all D DCS and all W frequency resources follows: Equation (22)

Recall frequencies and Av/2+1 ^were used f°^r pilot signal transmission and that each DCS d upshifted the impinging wave by d frequency resources. Also recall that channel HDcs_d,fc,(/_i,/_i+d)(ti) represents the communication channel between the BS and UE k for a signal transmitted at fa and received at f_i+d at time after being frequency shifted by d frequency resources by DCS d. Thus, channel H_DCSdiki(y_i ^_i+d)(t₁) can be estimated from the signal received at frequency resource f_1+d and channel H_DCSd,fc,(/_w/2+1,/_w/2+1+d)(ti) can be estimated from the signal received at frequency resource AV/2+I+U- H_Dcs_d,fc,(/₁,f_1+d)(^ti) ^and »DCS_d,k,(/_w/2+1,f_w/2+1+d) (^fi) ^are used t° denote the respective estimates. These estimates can be determined on the basis of the transmitted and received pilot signals using known techniques for channel estimation such as least-squares estimation or MMSE estimation. The function 'DCS^ combines the knowledge of H_DCSd,_k,_(/ii/i+d)(t₁) and H_DCSd,_{ki(/w/2+ii/w/2+i+d)}(t₁) via interpolation or extrapolation or some other means in order to output an estimate of H_DCSdik y^ , labeled as H_{DCSd k}^. An example of function Incs_d,f_M is the following:

Equation (23)

The assignment described by Equation (23) means that for all frequencies belonging to group the DCS channel estimate H_DCSdik^ will be approximated to be equal to HDcs_d,fc,(/₁,/_1+d)(ti) ^and for all frequencies belonging to group Q₂ the DCS channel estimate H_Dcs_d, k,f_M will be approximated to be equal to H_Dcs_d,fc,(/_W2+1,/_w/2+1+d)(ti) ■ This approximation is particularly accurate for the case where each group corresponds to a channel coherence band.

The channel estimates computed in the estimation step described above can be used to process the data signals received in E T_DliX (fy) in accordance with the resource allocation described in the allocation step of this embodiment and shown in Fig. 10. Thus, the embodiment for the data processing step is as described below.

Data processing step: Process received data

• Use the channel estimates computed in the estimation step to process the received data in fourth frequency resources E FonxCti) due to transmission of data in third frequency resources e DTxCii) ^as P^er the allocation step and the transmission step.

Embodiment 4

This is an embodiment for the case of channel estimation in two time slots (T = 2), wherein UEs share frequency resources for pilot signals.

Without loss of generality and for sake of simplicity to explain this embodiment, we further define and clarify the following notation and assumptions:

• There are W = 4(D/2 + 1) frequency resources fy./fy - >fw ■

• The spacing between adjacent frequency resources is the same and equal to y hence f_i+1 — ft = y. Thus, the frequency resources are evenly spaced in frequency.

• Notice constraint CO in Equation (2) is satisfied since WT = 8(D/2 + 1) > D + 1.

• Pilot signals for different UEs share the same frequency. For the downlink this is a straightforward scenario. For the uplink this means that UEs transmit pilot signals in shared frequency resources and utilize orthogonal pilot signals or semi-orthogonal within the same frequency resource.

Allocation step: Resource allocation for channel estimation for t_T = {fy, t₂}, i.e., for the two time slots T = 2:

• Divide the frequency resources into G groups, labeled as 9I,92' -9G, where each group represents a set of neighboring frequency resources. Each group can correspond to a channel coherence band. For simplicity to explain this embodiment, we choose the cardinality of each group, denoted as |//_a| for group Q_g, to be the same for all groups and equal to . Given the total W = ^(D/2 + 1) frequency resources, the two time slots

T = 2 and the group size , one can construct a total of G = 2 groups, labeled by assigning to each group the same number of frequency resources equal to IV/2 and creating groups (^and Q₂ as ordered sets with elements

The set T’PTXCG ) of first frequency resources for pilot signal transmission is chosen as the lowest frequency per group, thus

F PTX&T } ⁼ {fi>fw/2+i }■ Equation (24)

If we further define J^:prx(fT’9g^>) ^as the set of frequency resources for pilot signal transmission used at time t_T for group Q_g, then we have that Equation (25)

This assignment means that lowest frequency per group is used for pilot signal transmission as shown in Fig. 11.

The set T/_;i>_x(t_T ) of second frequency resources for pilot signal reception is chosen as the lowest D/2 + 1 frequencies per group, thus Equation (26)

If we further define ^PRx^^Qg) as the set of frequency resources for pilot signal reception used at time t_T group Q_g, then we have that

Equation (27) ? PRxttt&f) = {fw/2 + lifw/2 +2, — ’fw/2 +0/2 + 1}*

This assignment means that lowest D/2 + 1 frequencies per group are used for pilot signal reception as shown in Fig. 11.

Activate D/T = D/2 DCSs in time slot t_T = t_r. This means that half of the DCSs are active and half are inactive in slot t_T = t_r. The active DCS are d = 1, 2, D/2 and the inactive DCSs are d = D/2 + 1, D/2 + 2, , D. Hence, the active subset of the DCSs at time is defined as D'Ctf) = {1,2, ... , D/2 }. Each active DCSs d is assigned a frequency shift that upshifts the impinging signal by d frequency resources. Hence A/_d(t₁) = dy. where y is the spacing between adjacent frequency resources and is assumed in this embodiment to be the same between all adjacent frequency resources. Consequently, for a pilot signal transmitted at frequency resource ft during time slot t_1; the channel from DCSs d can be measured at frequency resource f_i+d. This is shown in Fig. 11, where it can for example be observed that for time slot and pilot signal transmitted at f_r, the contribution from DCS 1 is measured at A and so on such that the contribution from DCS D/2 is measured at f_D/₂₊₁.

Activate D/T = D /2 DCSs in time slot t_T = t₂. This means that half of the DCSs are active and half are inactive in slot t_T = t₂. Since half of the DCSs were already activated in t_x, then for t₂ the active DCSs are the ones that were not activated in t_x. The active DCSs in t₂ are d = D/2 + 1, D/2 + 2, ... , D and the inactive DCSs are d = 1,2, ... , D /2. Hence the roles of active and inactive are inversed with respect to what was assigned for A and the set of active DCS at time t₂ is defined as D'(A) = {D/2 + 1, D/2 + 2, ... , D}. Each active DCS d in t₂ is assigned a frequency shift that upshifts the impinging signal by d — D /2 frequency resources. Hence A/_d(t₂) = (d — D/2)~ y. wherein y is the spacing between adjacent frequency resources and is assumed in this embodiment to be the same between all adjacent frequency resources. Consequently, for a pilot signal transmitted at frequency resource fa during time slot t₂, the channel from DCS d > D/2 + 1 can be measured at frequency resource fi_+d-D/2- This is shown in Fig. 11 where it can for example be observed that for a pilot signal transmitted at in t₂ the contribution from DCS D/2 + 1 is measured at f₂ and so on such that the contribution from DCS D is measured at f_D/₂₊₁.

Constraint Cl in Equation 3 is satisfied since:

OPTIONALLY : At this point, half of the frequency resources are unused during time slots t_xand t₂, so one option is to use those frequency resources for data transmission as follows:

Define as the set of frequency resources for data transmission used at time t_T group Q_g. For two time slots A , t₂ and two groups Q₁, <j₂we define The groups are also shown in Fig. 11.

Define ^as the set of frequency resources for data reception used at time t_T group Q_g. For time slots fy , t₂ and two groups define

The groups are also shown in Fig. 11.

The set of third frequency resources for data transmission at time slot t_T is and the set of fourth frequency resources for data reception at time slot t_T is

Notice that the assignments defined by Equation (30) and Equation (31) satisfy constraint C2 in Equation (4) and constraint C3 in Equation (5). end for

The resource allocation for channel estimation and optional data transmission defined in the allocation step described above is communicated to involved devices and used for over the air transmission as described in the following transmission step.

Transmission step: Over the air transmission for channel estimation

• Perform signal exchange to inform the involved entities of the resource allocation described in the allocation step. Possible embodiments of signaling exchanges for downlink and uplink pilot signal exchange are provided later in Embodiments 6 and 7.

In a scenario of downlink pilot signal transmission, the resource allocation defined in this embodiment and illustrated in Fig. 11 is used as follows: At time slot t_x, the BS transmits pilot signals on G FpTxti), each UE receives pilot signals on and the BS uses G

?DTX (fi) to transmit data. The data can be for all UEs or for a single UE. The concerned UE or UEs receive this data on Attime slot t₂, the BS transmits pilot signals on G F_PTX(t₂), each UE receives pilot signals on G F_PRX(t₂) and the BS uses f_0J G T_DTXQt₂') to transmit data. The data can be for all UEs or for a single UE. The concerned UE or UEs receive this data on G ? DRX^Z)-

• In a scenario of uplink pilot signal transmission, the resource allocation defined in this embodiment and illustrated in Fig. 11 is used as follows: At time slot t_x, each UE transmits pilot signals on G

T'p-rx(ti). Different UEs use orthogonal pilot signals. The BS receives pilot signals on G

F_PRX (ti), one or several UEs transmit data on G T_DTX (t_x) and the BS receives this data on G ^DRx(h)- At time slot t₂, each UE transmits pilot signals on G FprxCh)- Different UEs use orthogonal pilot signals. The BS receives pilot signals G Fp_RX(t₂), one or several UEs transmit data on G F_DTX(t₂) and the BS receives this data on G FoRxCh)-

The signals received on frequency resources G T_PRXQt₁ ) at time slot and on frequency resources fu G F_PRX (t₂ ) at time slot t₂ due to the over the air transmission in the transmission step and using the resource allocation in the allocation step are used in the estimation step for channel estimation as follows.

Estimation step: Channel estimation

• For each UE k, estimate the non-DCS channel H_{o k}y^ for all W frequency resources A-/2- fw as follows: Equation (32)

Frequencies j\ and Av/2+1 ^were used f°^r pilot signal transmission and reception. Hence channels H_{o fe} (t_T) and H₀,fc,/_w/2+1 (t_T) can be directly estimated from the received signal using known techniques of channel estimation such as least-squares estimation and MMSE estimation at frequencies and Av/2+1 at time t_T. Their respective estimates are denoted as H_0;fcj’₁(t._r) and These estimates can be used as inputs to function I_OJ_M in Equation (32) which uses this information to estimate the non-DCS channel for all frequency resources fi’fi’ - ’fw f°^r UE k. Thus, function I_o is such that it combines the knowledge of H_{o fe} (t_T) obtained from all time slots and t₂ via interpolation or extrapolation or some other means in order to output an estimate of H_{o fe} . For example, the estimate H_{o fe} of can be calculated as follows:

The assignments described by Equation (33) mean that for all frequencies belonging to group the non-DCS channel estimate will be approximated by an average of the estimate H_{o kji}(t_T) computed at and t₂. For all frequencies belonging to group g₂, the non-DCS channel H_{o fe} will be approximated by an average of the estimate computed and t₂. This approximation is particularly accurate for the case where slots and t₂ are within the same coherence time and where each group corresponds to a channel coherence band.

For each UE k, estimate the DCS channel for all D DCS and all W frequency resources A, f₂, ■■■ , fw as follows:

Equation (34)

Frequencies fa and Av/2+1 ^were used f°^r pilot signal transmission. At time slot only DCSs d = 1, 2, ... , D/2 were activated and each active DCS d upshifted the impinging wave by d frequency resources. Channel H_{DCSd k (}y.^._+d)(t₁) represents the communication channel between the BS and UE k in slot of a signal transmitted at fa and received at fa_+d after being frequency shifted by d frequency resources by DCS d. Thus, channel H_{DCSd fe} ,/_1+d) (t_x) can be estimated from the signal received at frequency resource fa_+d and channel estimated from the signal received at frequency resource respective estimates.

At time slot t₂ only DCSs d = D/2 + 1, D/2 + 2, ... , D were activated and each active DCS d upshifted the impinging wave by d — D/2 frequency resources. Channel HDCSd,fc,(/iTi+d-D/2) (^t2) represents the propagation between the BS and UE k in slot t₂ of a signal transmitted at ft and received at fi+d-D/2 after being frequency shifted by d — D/2 frequency resources by DCS d. Thus, channel H_DCSd;fe;(y₁ ^_1+d_ ) can be estimated from the signal received at frequency resource A+d-0/2 and channel ^HDcs_d,fc,(/_W2+1,/_W2+1+d-D/2) (t2) can be estimated from the signal received at frequency resource are used to denote the respective estimates.

The function /DCS^ f°^r d < D/2 combines the knowledge of estimates and (t₁) via interpolation or extrapolation or some other means in order to output an estimate of H_{DCSd k} for d < D/2. Similarly, the function /Dcs_d,/_O) — D/2 + 1 combines the knowledge of estimates HDQS^^ ₂j(t₂) and

HDCS_d,fc,(/_w/2+1,/_W2+1+d-D/2) (t2) via interpolation or extrapolation or some other means in order to output an estimate of H_DCSdik^ for d > D/2 + 1. H_DCSdik ^ is used to denote the estimate of H_DCSdik y^ . Examples of functions of /Dcs_d,/_O) for d < D/2 and for and for DCS d > D/2 + 1 are the following: For DCS d < D/2 assign

Equation (35) and for DCS d > D/2 + 1 assign

HocSd.fc,^

= hcsa.fu (fi_DCSd,fc,(/₁,/_1+d-D/2) (t2), ^DCS_d,k,(f_w/₂₊₁,f_w/_2+1+d-D/₂) (^2) ) H_DCSd,_fe,₍y₁,_/1+d-D/2)(t₂) for all

^ocs_d,k,(f_W/₂₊₁,f_W/_2+1+d-D/₂') (/2) for all

Equation (36)

The assignments described in Equation (35) and Equation (36) mean that o For DCSs d < D/2 and for all frequencies belonging to group Q_r, the DCS channel HDCS^/G, will be approximated by the estimated fi_DCSd,fc,(y_1/1+d) (fy) o For DCSs d < D/2 and for all frequencies belonging to group Q₂. the DCS channel Hocsd.fc,^ will be approximated by the estimated (t₁) ■ o For DCSs d > D/2 + 1 and for all frequencies belonging to group Q_r, the DCS channel HDCSd.fc,^ will be approximated by the estimated o For DCSs d > D/2 + 1 and for all frequencies belonging to group Q₂. the DCS channel HDCSd-fc/o, ^{wil1 be} approximated by the estimated H_DCSd,_{ki(/w/2+ii/w/2+i+d-D/2)}(t₂).

These approximations are particularly accurate for the case where slots fy and t₂ are within the same coherence time and where each group corresponds to a channel coherence band.

The channel estimates computed in the estimation step described above can be used to process the data signals as per the embodiment for the data processing step below.

Optional data processing step: Process received data

• Use the channel estimates computed in the estimation step to process the data received in frequency resources E F_DRX(ti) due to transmission of data in frequency resources E F_DTx(ti ) in time slot fy and the data received in E ^DRX ^T) due to transmission of data in frequency resources E T_DTX(t₂ ) in time slot t₂.

Embodiment 5

This is an embodiment for the case of channel estimation in one time slot (T = 1), where UEs use orthogonal frequency resources for pilot signals. Without loss of generality and for sake of simplicity to explain this embodiment, we further define and clarify the following notation and assumptions:

• There are W = K(D + 1) frequency resources f_ltf₂,, - f_w .

• The spacing between adjacent frequency resources is the same and equal to y hence f_i+1 — ft = Y-

• Constraint CO in Equation (2) is satisfied since WT = K(D + 1) > D + 1.

• Pilot signals for different UEs are transmitted in different frequency resources.

• Chose the lowest K frequency resources as first frequency resources for pilot signal transmission Equation (37) and assign to UE k the frequency resource k for pilot signal transmission as shown in 12.

• Choose the entire K(D + 1) frequency resources as second frequency resources for pilot signal reception per coherence band, hence Equation (38) as shown in Fig. 12.

• At this point all the frequency resources are assigned for pilot signals. Hence, there are empty sets of frequency resources for data, ?_DTX = ?DRX ⁼ 0 and there is no data exchange in this embodiment.

• Activate D/T DCSs during the single time slot t_x. Since T = 1, all D DCSs are activated during the single time slot fy, thus the active subset of the DCSs D'(fy) = {1,2, ... , D }. For each DCS d = 1,2, ... , D, assign a frequency shift that upshifts the impinging signal by dK frequency resources. Thus A/_d(t₁) = dKy, where y is the spacing between adjacent frequency resources which, in this embodiment, is assumed to be the same between all adjacent frequency resources. Consequently, for a pilot signal transmitted at frequency resource the channel from DCS d can be measured at frequency resource f_M+aK- This is shown in Fig. 12, which illustrates that for a pilot signal transmitted at f_r, the contribution from DCS 1 is measured at f_1+K , the contribution from DCS 2 is measured at /₁₊₂z< and so on such that the contribution from DCS D is measured at f_1+DK.

• The above assignments satisfy constraint Cl in Equation (3). end for

The resource allocation for channel estimation defined in the allocation step is communicated to involved devices and used for over the air transmission as described in the following transmission step.

Transmission step: Over the air transmission for channel estimation

Perform signal exchange to inform the involved entities the resource allocation described in the allocation step. Possible embodiments of signaling exchanges for downlink and uplink pilot signal exchange are provided later in Embodiments 6 and 7. • Perform over the air transmission during the single time slot and via the IV frequency resources by using the time and frequency resource allocation scheme defined in the allocation step.

• In a scenario of downlink pilot signal transmission, the resource allocation defined in this embodiment and illustrated in Fig. 12 is used as follows: The BS transmits pilot signals on frequencies G FpTxCh ) and the pilot signals for UE k are transmitted and received on frequencies f_k,f_k+K,f_k+2K, - ,f_k+DK-

• In a scenario of uplink pilot signal transmission, the resource allocation defined in this embodiment and illustrated in Fig. 12 will be used as follows: UE k transmits pilot signals on f_k and the pilot signals from UE k are received by the BS on frequencies fk> fk+K> fk+2K> — > fk+DK-

The signals received after the over the air transmission as in the transmission step and using the resource allocation in the allocation step are used in the estimation step for channel estimation as follows.

Estimation step: Channel estimation

• For each UE k, estimate the non-DCS channel H_{o k}y^ for all W frequency resources A-/2- fw as follows: Equation (39)

Frequency f_k was used for pilot signal transmission and reception for UE k. Hence, the non- DCS channel H_o ,fc,/_k(ti) f°^r UE k can be directly estimated from the received signal at frequency f_k at the single time slot t_x, as shown in Fig. 12. This estimate is denoted as x) and is used as input to function /₀^ which uses this information to estimate, via interpolation or extrapolation or some other means, the non-DCS channel for all frequency resources f_r,f₂, - ,fw f°^r UE k. The output of function /_Oy is an estimate of H_o denoted An example of function l₀ ^ is the following: Equation (40)

The assignment described by Equation (40) means that for all frequencies, the non-DCS channel estimate H_{o k} y^ is set to be equal to H_{o k} ^_fc(t₁). The function described by Equation (40) is particularly accurate for the case where the frequency resources are within the same coherence band. For each UE k, estimate the DCS channel H_DCS (t_x) for all D DCSs and all W frequency resources A, f₂, ■■■ , fw ^as follows: Equation (41)

Frequency f_k was used for UE fc’s pilot signal transmission and each DCS d upshifted the impinging wave by dK frequency resources. Channel H_DCSd ,k,(f_k,f_k+dK) (U) represents the communication channel between the BS and UE k for a signal transmitted at f_k and received at fk+dK at time after being frequency shifted by dK frequency resources by DCS d. Thus channel H_{DCS fe;(}y )(t_x) can be estimated from the signal received at frequency resource fk+dK and H_DCs_d,fc,(/_k,/_k+d/f) (U) is used to denote the respective estimate. The function I_DCs_d,f_M uses the knowledge of to compute via interpolation or extrapolation or some other means an estimate of H_DCSdik^, labeled as H_DCSdik^. An example of function hcsa.fv, is the following:

Equation (42)

The assignment described by Equation (42) means that for all frequencies the DCS channel estimate fi_DCSd;fe;/(U will be approximated by H_{DCSd k (/ki/k+d/f)}(t₁). This approximation is particularly accurate for the case where the frequency resources are within the same coherence band.

Embodiment 6: Signaling exchange for Downlink

In this embodiment, a case is described wherein the over the air transmission and reception of the transmission step of the algorithms described above takes place in a downlink configuration.

Fig. 13 illustrates exchanges between a BS, a DCS, and a UE in a downlink configuration wherein the transmission of pilot signals is performed by the BS and reflected pilot signals are obtained when the pilot signals from the BS are reflected at the DCS. In implementations, a plurality of DCSs and a plurality of UEs can be provided, wherein each DCS and each UE can be operated as illustrated in Fig. 13.

At step 1301, the allocation step of any of the algorithms described above is performed. As shown in Fig. 13, the allocation step 1301 can be performed at the BS.

Thereafter, at step 1302, the BS 204 can transmit information representative of the allocated resources to the DCSs and the UEs. The transmitted information can include, in particular, information on which DCS are to be activated, information representative of the respective frequency shift assigned to each DCS, and information representative of the first frequency resources used for the transmission of the pilot signals. In some implementations, different information can be transmitted to the DCSs and the UEs. For example, the DCSs can be provided with information relating to the respective frequency shifts and the UEs can additionally be provided with information relating to the first frequency resources. In such embodiments, step 1302 can include substep 1302a of transmitting information to the DCSs and substep 1302b of transmitting information to the UEs. In other implementations, the DCSs and the UEs can be provided with the same information.

The present disclosure is not limited to implementations wherein the allocation step is carried out at the BS. In alternative implementations, the allocation step 1301 can be carried out at a DCS or at a UE. In this case, at step 1302, the entity (DCS orUE) that has carried out the allocation step 1301 communicates the information representative of the allocated resources to the other entities (BS, UEs and DCSs).

Then, at step 1303, the scattering patterns of the DCSs are configured with the received frequency shift information, and at step 1304, the UEs are configured with the received resource allocation information.

Then, at step 1305, the transmission step of any of the algorithms described above is performed. The BS transmits pilot signals and, optionally, data signals, and reception of signals at the UEs takes place. The signals received at the UEs contain some components that are due to the scattering and frequency shifting of the DCSs as designated in the allocation step 1301.

Then, at step 1306, the estimation step of channel estimation and the optional data processing step of any of the algorithms described above are performed at each UE. For this purpose, the signal received at each UE is used to perform channel estimation at each UE. The computed channel estimates can be used for subsequent communication between the BS and the UEs (not shown on the figure) or optionally be fed back as channel state information (CSI) to the BS at step 1307 which can further use and aggregate the information from all UEs as a further improvement of the estimation step at step 1308.

Embodiment 7: Signaling exchange for Uplink

In this embodiment, a case is described wherein the over the air transmission and reception of the transmission step of the algorithms described above takes place in an uplink configuration.

Fig. 14 illustrates exchanges between BS, a DCS, and a UE wherein the UEs send pilot signals and data signals in accordance with the allocation step of any of the algorithms described above, and the BS receives the signals, which include reflected pilot signals that are obtained upon reflection of the pilot signals from the UEs at the DCSs. In implementations, a plurality of DCSs and a plurality of UEs can be provided, wherein each DCS and each UE can be operated as illustrated in Fig. 14. At step 1401, the allocation step of performing resource allocation of any of the algorithms described above is performed. As shown in Fig. 14, the allocation step 1401 can be performed by the BS. Thereafter, at step 1402, information representative of the allocated resources is transmitted. The transmitted information can include, in particular, information which DCSs are to be activated, information representative of the respective frequency shift assigned to each DCS, and information representative of the first frequency resources used for the transmission of the pilot signals. Similar to step 1302 in embodiment 6, in some implementations, step 1402 can include substep 1402a of transmitting information to the DCSs and substep 1402b of transmitting information to the UEs. Steps 1401, 1402 can be performed similar to steps 1301, 1302 of embodiment 6 described above with reference to Fig. 13. In particular, steps 1401, 1402 can be performed by the BS, as shown in Fig. 14, or by another entity, for example a DCS or a UE.

Then, at step 1403, the scattering patterns of the DCSs are configured with the received frequency shift information, and at step 1404, the UEs are configured with the received resource allocation information.

Then, at step 1405, the BS can send a training request to the UEs, wherein the BS requests the transmission of the pilot signals and, optionally, the transmission of data from the UEs.

In response thereto, at step 1406, the transmission step of any of the algorithms described above is performed, wherein the UEs transmit pilot signals and, optionally, data signals, and reception of signals at the BS takes place. The signals received at the BS contain some components that are due to the scattering and frequency shifting of the DCSs, as designated in the allocation step 1401.

At step 1407, the signal received at the BS is used to perform channel estimation in accordance with the estimation step of any of the algorithms described above, and to optionally process data as in the data processing step of any of the algorithms described above. The computed channel estimates can be used for subsequent communication between the BS and the UEs (not show in in the figure).

Embodiment 8

The steps in Algorithm 1 can also be applied to a single DCS composed of S scattering elements by creating D disjoint groups of scattering elements. For example by assigning S/D disjoint scattering elements per group. Our embodiments above can be applied by treating the D disjoint groups as different DCSs. Furthermore the scattering elements that form the groups can be co-located or distributed.

The foregoing descriptions are merely specific implementations of this application, but are not intended to limit the scope of protection of this application. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in this application shall fall within the scope of protection of this application. Therefore, the scope of protection of this application shall be subject to the scope of protection of the claims.

Claims

1. A communication arrangement (200) for communication over a plurality of frequency resources, comprising: a plurality of digitally controllable scatterers, DCSs (201, 202, 203), configmed for frequency shifting electromagnetic radiation upon reflection thereon; assignment circuitry (306) for assigning a respective frequency shift to each DCS of an active subset of the plurality of DCSs (201, 202, 203), and for assigning at least one first frequency resource of the plurality of frequency resources to one or more first communication nodes, CNs, for transmission of a respective pilot signal; wherein the frequency shifts assigned to the DCSs of the active subset of DCSs are different from each other, wherein the plurality of frequency resources further comprises a plurality of second frequency resources, and wherein the at least one first frequency resource and the frequency shifts assigned to the DCSs of the active subset of DCSs are selected such that upon reflection of each pilot signal at each DCS of the active subset of DCSs, a reflected pilot signal having a frequency within a respective second frequency resource of the plurality of second frequency resources is obtained; and channel estimation circuitry (307) configured to obtain first reception information from one or more second CNs, the first reception information being based on a reception of the reflected pilot signals by the one or more second CNs in the plurality of second frequency resources, and to estimate, for at least one DCS of the active subset of the plurality of DCSs (201, 202, 203), at least one respective communication channel between at least one of the one or more first CNs and at least one of the one or more second CNs via the at least one DCS of the active subset of the plurality of DCSs (201, 202, 203) on the basis of the first reception information.

2. The communication arrangement (200) according to claim 1, wherein the plurality of frequency resources comprises one or more groups of frequency resources, wherein each group of frequency resources comprises at least one first frequency resource and one or more second frequency resources, and wherein the frequency shifts assigned to the DCSs of the active subset of DCSs are selected such that, for each first frequency resource, upon reflection of each pilot signal transmitted by the one or more first CNs in the respective first frequency resource at each DCS of the active subset of DCSs, a reflected pilot signal having a frequency within the one or more second frequency resources of the same group of frequency resources is obtained.

3. The communication arrangement (200) according to claim 2, wherein each group of frequency resources comprises two or more second frequency resources.

4. The communication arrangement (200) according to claim 2 or 3, wherein each group of frequency resources corresponds to a channel coherence band.

5. The communication arrangement (200) according to any of claims 2 to 4, wherein, in each group of frequency resources, the at least one first frequency resource and the one or more second frequency resources of the respective group of frequency resources form a subset of the frequency resources of the respective group of frequency resources that are consecutive in frequency.

6. The communication arrangement (200) according to any of claims 2 to 5, wherein the channel estimation circuitry (307) is configured to estimate, for each group of frequency resources, at least one respective communication channel between at least one of the one or more first CNs and at least one of the one or more second CNs via the at least one DCS of the active subset of the plurality of DCSs (201, 202, 203).

7. The communication arrangement (200) according to any of claims 2 to 6, wherein the one or more first CNs are a plurality of first CNs, wherein each group of frequency resources comprises one first frequency resource that is assigned to each of the plurality of first CNs for transmission of the respective pilot signal, and wherein the pilot signals transmitted by the plurality of first CNs comprise at least one of orthogonal and semi-orthogonal signals within the one first frequency resource of each group of frequency resources.

8. The communication arrangement (200) according to claim 7, wherein the pilot signals transmitted by the plurality of first CNs are orthogonal in at least one of time and code.

9. The communication arrangement (200) according to any of claims 2 to 8, wherein the one or more first CNs are a plurality of first CNs, each group of frequency resources comprises a plurality of first frequency resources, and, in each group of frequency resources, a different first frequency resource of the plurality of first frequency resources of the respective group is assigned to each of the plurality of first CNs.

10. The communication arrangement (200) according to any of the preceding claims, wherein the active subset of the plurality of DCSs (201, 202, 203) comprises all of the plurality of DCSs (201, 202, 203).

11. The communication arrangement (200) according to any of claims 1 to 9, wherein: the plurality of DCSs (201, 202, 203) are further configured for switching between an active state and an inactive state, wherein each DCS of the plurality of DCSs (201, 202, 203) that is in the inactive state provides a weaker reflection of the pilot signals from the one or more first CNs to the one or more second CNs than when it is in the active state; the communication arrangement (200) further comprises circuitry for switching, in each of a plurality of time intervals, a different subset of the plurality of DCSs (201, 202, 203) into the active state and for switching the other DCSs of the plurality of DCSs (201, 202, 203) into the inactive state, wherein, in each of the plurality of time intervals, the active subset of the DCSs is formed by the subset of the plurality of DCSs (201, 202, 203) that are in the active state in the respective time interval.

12. The communication arrangement (200) according to claim 11 , wherein each of the plurality of DCSs (201, 202, 203) is in the active state in at least one of the plurality of time intervals.

13. The communication arrangement (200) according to claim 11 or 12, wherein: the assignment circuitry (306) is configmed to assign, for each of the plurality of time intervals, a respective frequency shift to each DCS of the subset of the DCSs that are in the active state in the respective time interval; and the channel estimation circuitry (307) is configmed to estimate, for each of the plurality of time intervals, a respective communication channel from at least one of the one or more first CNs to at least one of the one or more second CNs via at least one DCS of the subset of the DCSs that are in the active state in the respective time interval on the basis of the first reception information that is obtained for the respective time interval.

14. The communication arrangement (200) according to any of claims 11 to 13, wherein at least a part of the plurality of DCSs (201, 202, 203) comprises: a plurality of scattering elements (407), at least a part of the plurality of scattering elements (407) being adapted such that a reflection phase shift thereof is electronically controllable; and circuitry (405) for controlling the reflection phase shifts of said at least a part of the plurality of scattering elements (407) such that in the active state of the respective DCS and in the inactive state of the respective DCS, the pilot signals are scattered in specific directions wherein, in the inactive state, less energy is scattered towards the second CNs.

15. The communication arrangement (200) according to any of claims 11 to 13, wherein at least a part of the plurality of DCSs (201, 202, 203) comprises: a plurality of scattering elements (407), at least a part of the plurality of scattering elements being adapted such that a reflection amplitude thereof is electronically controllable; and circuitry (409) for controlling the reflection amplitude of said at least a part of the plurality of scattering elements (407) such that in the active state of the respective DCS, the reflection amplitude of said at least a part of the plurality of scattering elements (407) is greater than in the inactive state.

16. The communication arrangement (200) according to any of the preceding claims, wherein the plurality of frequency resources further comprises at least one third frequency resource that is a different frequency resource than the at least one first frequency resource and the plurality of second frequency resources, and wherein the assignment circuitry (306) is configured to assign the at least one third frequency resource to the one or more first CNs and the one or more second CNs for data transmission.

17. The communication arrangement (200) according to claim 16, wherein the plurality of frequency resources further comprises a plurality of fourth frequency resources that are different frequency resources than the first, second and third frequency resources, and wherein the fourth frequency resources are selected such that, for each of the at least one third frequency resource, a data transmission signal having a frequency in the respective third frequency resource is frequency shifted into a respective one of the plurality of fourth frequency resources upon reflection at each DCS of the active subset of the plurality of DCSs (201, 202, 203).

18. The communication arrangement (200) according to claim 17, wherein the plurality of frequency resources comprises one or more groups of frequency resources, each group of frequency resources corresponding to a channel coherence band, and wherein each group of frequency resources comprises at least one third frequency resource and at least one fourth frequency resource.

19. The communication arrangement (200) according to any of the preceding claims, wherein at least a part of the plurality of DCSs (201, 202, 203) comprises: a plurality of scattering elements (407), at least a part of the plurality of scattering elements being adapted such that a reflection phase shift thereof is electronically controllable; and circuitry (406) for applying a temporal variation of the reflection phase shift of said at least a part of the plurality of scattering elements (407), wherein a frequency of the temporal variation corresponds to the frequency shift assigned to the respective DCS.

20. The communication arrangement (200) according to claim 19, wherein the assignment circuitry (306) is further configmed to assign a respective scattering pattern to each DCS of the active subset of the plurality of DCSs (201, 202, 203).

21. The communication arrangement (200) according to any of the preceding claims, wherein the assignment circuitry (306) is provided at one of the one or more first CNs, and the one of the one or more first CNs is configmed to transmit information representative of the respective frequency shift assigned to each DCS of the active subset of the plurality of DCSs (201, 202, 203) and to transmit information representative of the at least one first frequency resource to the one or more second CNs.

22. The communication arrangement (200) according to claim 21, wherein the assignment circuitry (306) is further configured to transmit the information representative of the at least one first frequency resource to the plurality of DCS (201, 202, 203).

23. The communication arrangement (200) according to claim 21 or 22, wherein the one of the one or more first CNs is a base station (204).

24. The communication arrangement (200) according to any of claims 21 to 23, wherein the channel estimation circuitry (307) is provided at at least one of the one or more second CNs.

25. The communication arrangement (200) according to claim 24, wherein the at least one of the one or more second CNs is configured to transmit channel state information that is based on the estimation performed by the channel estimation circuitry (307) to the one of the one or more first CNs.

26. The communication arrangement (200) according to any of the preceding claims, wherein the assignment circuitry (306) and the channel estimation circuitry (307) are provided at one of the one or more second CNs, the one of the one or more second CNs being configured to transmit information representative of the respective frequency shift assigned to each DCS of the active subset of the plurality of DCSs and information representative of the at least one first frequency resource to the one or more first CNs.

27 '. The communication arrangement (200) according to claim 26, wherein the one of the one or more second CNs is a base station (204).

28. The communication arrangement (200) according to any of the preceding claims, wherein the plurality of frequency resources are evenly spaced in frequency, and wherein at least a part of the frequency shifts assigned to the active subset of the plurality of DCSs (201, 202, 203) is an integer multiple of a frequency spacing between adjacent frequency resources of the plurality of frequency resources.

29. The communication arrangement (200) according to any of the preceding claims, wherein the frequency shifts assigned to the active subset of the plurality of DCSs (201, 202, 203) are upward shifts to a higher frequency.

30. The communication arrangement (200) according to any of the preceding claims, wherein the plurality of second frequency resources are different frequency resources than the at least one first frequency resource, wherein the channel estimation circuitry (307) is further configured to obtain second reception information from the one or more second CNs, the second reception information being based on a reception of the pilot signals by the one or more second CNs in the at least one first frequency resource, and wherein the channel estimation circuitry (307) is further configured to estimate at least one non-DCS communication channel between at least one of the one or more first CNs and at least one of the one or more second CNs on the basis of the second reception information.

31. A method of communication over a plurality of frequency resources, comprising: assigning (807) a respective frequency shift to each digitally controllable scatterer, DCS, of an active subset of a plurality of DCSs (201, 202, 203); assigning (808) at least one first frequency resource of the plurality of frequency resources to one or more first communication nodes, CNs, for transmission of a respective pilot signal; wherein the frequency shifts assigned to the DCSs of the active subset of DCSs are different from each other, wherein the plurality of frequency resources further comprises a plurality of second frequency resources, and wherein the at least one first frequency resource and the frequency shifts assigned to the DCSs of the active subset of DCSs are selected such that upon reflection of each pilot signal at each DCS of the active subset of DCSs with the frequency shift assigned to the respective DCS, a reflected pilot signal having a frequency within a respective second frequency resource of the plurality of second frequency resources is obtained; transmitting (812), in the at least one first frequency resource, a respective pilot signal by each of the one or more first CNs; receiving (813), in the plurality of second frequency resources, the reflected pilot signals at each of one or more second CNs; and estimating (816), for at least one DCS of the active subset of the plurality of DCSs, at least one respective communication channel between at least one of the one or more first CNs and at least one of the one or more second CNs via the at least one DCS of the active subset of the plurality of DCSs on the basis of the reflected pilot signals received at the one or more second CNs.

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