WO2023066475A1

WO2023066475A1 - Irs selection for improving the spatial multiplexing capability of a link

Info

Publication number: WO2023066475A1
Application number: PCT/EP2021/079065
Authority: WO
Inventors: Samer Bazzi; Malte Schellmann; Wen Xu
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2021-10-20
Filing date: 2021-10-20
Publication date: 2023-04-27
Also published as: EP4406146A1

Abstract

This disclosure is concerned with improving the spatial multiplexing capability of a link between two communication devices, for example, in case of a direct line of sight (LOS) link. The disclosure presents a way to use intelligent reflecting surfaces (IRSs) for achieving this. The disclosure proposes selecting a subset of IRSs from all available IRSs in the communication environment of the two communication devices. Then, for each respective IRS in the subset, first channel estimation information can be obtained for an IRS augmented channel including the direct link and indirect link via the respective IRS between the two communication devices. Using the first channel estimation information, antenna configuration information can be given to each IRS of the subset, and then second channel estimation information can be obtained for each IRS augmented channel. Based thereon, one IRS of the subset may be selected for further communication between the two communication devices.

Description

IRS SELECTION FOR IMPROVING THE SPATIAL MULTIPLEXING CAPABILITY

OF A LINK

TECHNICAL FIELD

The present disclosure is concerned with improving the spatial multiplexing capability of a link between two communication devices, for example, when the link is a direct line of sight (LOS) link between the two communication devices. The disclosure proposes a way to use an intelligent reflecting surface (IRS) for achieving this improvement. The disclosure presents in this regard processing devices for improving the spatial multiplexing capability of the link between a first communication device and a second communication device, corresponding methods, and a computer program.

BACKGROUND

When a link between two communication devices, for instance, between a transmit-receive- point (TRP) and a user equipment (UE), exhibits a pure or very strong LOS link component, the rank of a corresponding channel matrix of a channel of the link will be 1. In this case, only one data stream can be transmitted per time and/or frequency slot between the two communication devices, regardless of the number of antennas available at the TRP and the UE. In other words, the spatial degrees of freedom cannot be exploited for multiplexing in this case, due to the inherent highly correlated channel.

Ways to improve the spatial multiplexing capability of such a link between the two communication devices would be beneficial, in particular, since this would allow increasing the achievable data rate over the link.

SUMMARY

Intelligent reflecting surfaces (IRSs) are emerging as a potential key technology for future wireless communication systems. An IRS typically comprises many passive and cheap antenna elements (in the order of 100s or 1000s of such antenna elements), which can be configured to reflect incoming communication signals into a desired direction (or into multiple directions) in a full duplex fashion, by applying corresponding phase shifts to each of the antenna elements. IRSs can be used for various use cases, such as coverage extension or signal-to-noise-ratio (SNR) maximization. This disclosure generally exploits another use case for IRSs, namely for channel matrix rank improvement, in order to improve the spatial multiplexing capability of a link, particularly of a LOS link. It may be understood that if an IRS were present in the vicinity of, for instance, the TRP and the UE in the above-mentioned example of the two communication devices communicating over the link, this IRS could be configured to provide an additional, especially optimized, communication path (an additional link) between the TRP and the UE. As a result, an IRS augmented channel is formed comprising the TRP-UE direct link plus the TRP-IRS-UE indirect link, and a rank of a channel matrix of this IRS augmented channel will increase compared to the channel matrix of the direct TRP-UE link alone. This would allow more than one data stream to be transmitted per time and/or frequency slot from the TRP to the UE, and would thereby increase the achievable data rate.

Clearly, however, future systems will not deploy only a single IRS, but rather a multitude of IRSs would likely be deployed in a given area or setup. Such a setup may be an industry 4.0 smart factory indoor setup, wherein many IRSs may be mounted to walls, for instance, as illustrated in FIG. 1. Alternatively, such a setup may also be an outdoor cellular scenario with many IRSs mounted on, e.g., buildings, as illustrated in FIG. 2 (taken from “How to Deploy Intelligent Reflecting Surfaces in Wireless Network: BS-side, User-side, or Both Sides?" by You et al.; https://arxiv.org/abs/2012.03403). For the indoor setup of FIG. 1, there may be UEs (“machines”), wherein each UE may be equipped with one or more high antennas (e.g., reaching above the typical height of other machines or blocking objects), and may thus experience a LOS link to a TRP or Base Station (BS), at least with a high probability. For the outdoor setup of FIG. 2, due to densification (e.g., an increased number of TRPs per km²), there is a high LOS link probability between a UE and a TRP, due to shorter TRP-UE distances.

In both setups, for a given TRP-UE link where both the TRP and the UE have multiple antennas, the question arises, which IRS in the vicinity of the TRP and the UE would result in the largest achievable data rate.

In view of the above, this disclosure is concerned with improving the spatial multiplexing capability of a link between two communication devices by using an IRS. An objective is thereby to increase, or even to maximize, the achievable data rate between the two communication devices. Thus, an objective is to find or select, with an acceptable training and signaling overhead, a certain IRS out of an available set of IRSs, which allows maximizing the achievable rate between the two communication devices.

One possible way to achieve the above objectives could be to simply calculate, based on the known channels between, for example, the UE, the IRS, and the TRP, the achievable rate corresponding to each IRS in the system, and then to choose the IRS that results in the largest achievable rate. However, this entails training and estimating corresponding IRS-UE and IRS- TRP channels for each IRS in the vicinity of the TRP and UE. Notably, channel estimation is typically done with reference signals (RS), which incurs an overhead that scales with the number of IRS antennas. Estimating all channels of all IRSs in the system would thus consume a lot of time and/or frequency resources, and would result in a huge signaling and training overhead, which could possibly result in large degradations of the net throughput, and thus should be avoided.

This disclosure achieves the above and other objectives by the solutions described in the enclosed independent claims. Advantageous implementations of the embodiments of the invention are further defined in the dependent claims.

A first aspect of this disclosure provides a processing device for improving a spatial multiplexing capability of a channel between a first communication device and a second communication device, the processing device being configured to: select a subset of IRSs from a set of IRSs available in a communication environment of the first and the second communication device, wherein the subset of IRSs is selected based on position information and antenna array information of both the second communication device and each IRS in the set of IRSs; and for each respective IRS in the subset of IRSs, the processing device being further configured to: obtain first channel estimation information for a channel including the link between the first and the second communication device and an additional link between the first and the second communication device via the respective IRS; and provide antenna configuration information to the respective IRS, wherein the antenna configuration information is based on the first channel estimation information obtained for the respective IRS.

The link between the first and the second communication device is a direct link, and may be a LOS link. By pre-selecting the subset of IRSs from the set of all available IRSs, by then further estimating for each IRS in the subset the corresponding IRS augmented channel, and by then further configuring each IRS based on this channel estimation, the selection of a certain IRS, which maximizes the data rate, becomes possible with acceptable training and signaling overhead. Thus, the processing device of the first aspect enables an improvement of the spatial multiplexing capability of the link between the first and the second communication device by using an IRS.

The selection of the subset may be done based on calculations, i.e., without performing any channel estimation and without sending RS. That is, the processing device may calculate the subset of IRSs by using the received position information and antenna array information. For instance, the processing device may calculate an IRS augmented channel for each available IRSs in the communication environment by using the corresponding position information and antenna array information, and may then further calculate an achievable rate for each calculated IRS augmented channel. Then, the subset of IRSs may be selected by the processing device by including those IRS into the subset, which result in the highest achievable rates. For example, all IRSs that result in a calculated rate, which is higher than a determined threshold rate, may be included into the subset. Alternatively, a predetermined number of IRSs may be included into the subset, namely those IRSs resulting in the highest calculated rates. As another example, all or some of the IRSs within a certain distance from the first and second communication devices may form the subset. Combinations of these criteria may be combined. The IRS augmented channels may then be calculated by calculating a channel for each direct link and a channel for each sub-link comprised in the IRS augmented channel. That is, a channel for the direct link between the first communication device and the second communication device, a channel for the direct link (sub-link) between the first communication device and the respective IRS, and a channel for the direct link (sub-link) between the respective IRS and the second communication device.

In an implementation form of the first aspect, the processing device is configured to obtain the first channel estimation information via: estimating the channel; or receiving the first channel estimation information from the second communication device.

For example, the channel can either be estimated on the side of the first communication device (e.g., based on one or more RS sent from the second communication device to the first communication device), or can be estimated on the side of the second communication device (e.g., based on one or more RS sent from the first communication device to the second communication device).

In an implementation form of the first aspect, the processing device is configured to estimate the channel based on one or more RS transmitted from the second communication device to the first communication device.

In an implementation form of the first aspect, the processing device is further configured to, after providing the antenna configuration information to the respective IRS: receive, from the second communication device, second channel estimation information for the channel estimated for the respective IRS.

The second channel estimation information may be estimated, by the second communication device, based on one or more RS sent from the first to the second communication device after the IRSs in the subset of IRSs have been configured with an antenna configuration according to the antenna configuration information. For instance, each antenna element of the respective IRS may have been configured with a phase shift and amplitude.

In an implementation form of the first aspect, the processing device is further configured to select a certain IRS from the subset of IRSs for further communication between the first and the second communication device, wherein the certain IRS is selected based on the second channel estimation information for each respective IRS in the subset of IRSs.

The certain IRS may be the one out of all the available IRSs, which maximizes the data rate between the first and the second communication device. Thus, the spatial multiplexing capability of the link between the two communication devices is improved by using an optimally selected IRS.

In an implementation form of the first aspect, the processing device is further configured to: provide, to the certain IRS selected from the subset of IRSs, an indication to keep the previously provided antenna configuration information; and/or provide, to each IRS not selected from the subset of IRSs, an indication to revoke the previously provided antenna configuration information. In an implementation form of the first aspect, the processing device is further configured to obtain the position information and antenna array information of both the second communication device and each IRS in the set of IRSs from at least one of: a network device, one or more IRSs in the set of IRSs, and the second communication device.

In an implementation form of the first aspect, the processing device is further configured to provide, to the second communication device, IRS information indicating the number of IRSs selected from the set of IRSs.

Thus, the second communication device may know, for how many and for which IRS the IRS augmented channel may be probed, i.e. first and second channel estimation information, or only the second channel estimation information may be obtained and fed back to the first communication device.

In an implementation form of the first aspect, the processing device is further configured to provide, to the second communication device along with the IRS information, RS information indicating the one or more RS.

In an implementation form of the first aspect, antenna array information comprises at least one of a number of antennas, an antenna pattern, an antenna layout, and an antenna spacing.

The antenna array information may influence the achievable data rate (e.g., a higher rate may be achieved for an IRS having more antennas and/or having a larger antenna spacing). Thus, the selection of the subset of IRSs from the available IRSs may reduce the total number of IRSs to be trained, while ensuring that the IRS resulting in the highest rate may be selected in the end.

In an implementation form of the first aspect, position information comprises at least one of: a location and an orientation in the communication environment of the first and the second communication device.

The position information may influence the achievable data rate (e.g., a higher rate may be achieved for an IRS being optimally oriented for conveying communication signals between the first and the second communication device). Thus, the selection of the subset of IRSs from the available IRS may reduce the total number of IRSs to be trained, while ensuring that the IRS resulting in the highest data rate may be selected in the end.

In an implementation form of the first aspect, antenna configuration information comprises at least one of a phase shift and an amplitude for each of a plurality of antenna elements of the respective IRS.

In an implementation form of the first aspect, second channel estimation information comprises a channel quality indicator for each of a plurality of spatially multiplexed streams supported by the channel.

This provides a basis for the first communication device to select the certain IRS that results in the highest rate.

In an implementation form of the first aspect, the second channel estimation information is based on one or more secondary RS, which are different than the one or more RS transmitted from the second communication device to the first communication device.

In an implementation form of the first aspect, the processing device is or is included in the first communication device.

In an implementation form of the first aspect, the first communication device is a network device, for example, a TRP; and/or the second communication device is a terminal device, for example, UE.

A second aspect of this disclosure provides a processing device for improving a spatial multiplexing capability of a link between a first communication device and a second communication device, the processing device being configured to: receive, from the first communication device, IRS information indicating a number of IRSs selected from a set of IRSs available in the communication environment of the first and the second communication device; and for each respective IRS in the subset of IRSs, the processing device being further configured to: provide, to the first communication device, first and second channel estimation information, or only the second channel estimation information, for a channel including the link between the first and the second communication device and an additional link between the first and the second communication device via the respective IRS.

By obtaining and providing the first and/or the second channel information to the first communication device, the processing device of the second aspect enables that the first communication device (or the processing device of the first aspect) may select the certain IRS achieving the highest rate with a reasonable overhead.

In an implementation form of the second aspect, the first and/or the second channel estimation information is based on respectively one or more primary and/or secondary RS transmitted from the first communication device to the second communication device.

In an implementation form of the second aspect, the processing device is further configured to: receive, from the first communication device, RS information indicating one or more RS; and if providing only the second channel estimation information to the first communication device: send, for each respective IRS in the subset of IRSs, the one or more primary RS to the first communication device.

In an implementation form of the second aspect, the processing device is further configured to: provide position information and antenna array information of the second communication device to the first communication device.

In an implementation form of the second aspect, the processing device is or is included in the second communication device.

A third aspect of this disclosure provides a method for improving a spatial multiplexing capability of a link between a first communication device and a second communication device, the method comprising: selecting a subset of IRSs from a set of IRSs available in a communication environment of the first and the second communication device, wherein the subset of IRSs is selected based on position information and antenna array information of both the second communication device and of each IRS in the set of IRSs; and for each respective IRS in the subset of IRSs, the method further comprising: obtaining first channel estimation information for a channel including the link between the first and the second communication device and an additional link between the first and the second communication device via the respective IRS; and providing antenna configuration information to the respective IRS, wherein the antenna configuration information is based on the first channel estimation information obtained for the respective IRS.

In an implementation form of the third aspect, the method comprises obtaining the first channel estimation information via: estimating the channel; or receiving the first channel estimation information from the second communication device.

In an implementation form of the third aspect, the method comprises estimating the channel based on one or more RS transmitted from the second communication device to the first communication device.

In an implementation form of the third aspect, the method comprises, after providing the antenna configuration information to the respective IRS: receiving, from the second communication device, second channel estimation information for the channel estimated for the respective IRS.

In an implementation form of the third aspect, the method further comprises selecting a certain IRS from the subset of IRSs for further communication between the first and the second communication device, wherein the certain IRS is selected based on the second channel estimation information for each respective IRS in the subset of IRSs.

In an implementation form of the third aspect, the method further comprises providing, to the certain IRS selected from the subset of IRSs, an indication to keep the previously provided antenna configuration information; and/or providing, to each IRS not selected from the subset of IRSs, an indication to revoke the previously provided antenna configuration information.

In an implementation form of the third aspect, the method further comprises obtaining the position information and antenna array information of both the second communication device and each IRS in the set of IRSs from at least one of: a network device, one or more IRSs in the set of IRSs, and the second communication device. In an implementation form of the third aspect, the method further comprises providing, to the second communication device, IRS information indicating the number of IRSs selected from the set of IRSs.

In an implementation form of the third aspect, the method further comprises providing, to the second communication device along with the IRS information, RS information indicating the one or more RS.

In an implementation form of the third aspect, antenna array information comprises at least one of a number of antennas, an antenna pattern, an antenna layout, and an antenna spacing.

In an implementation form of the third aspect, position information comprises at least one of: a location and an orientation in the communication environment of the first and the second communication device.

In an implementation form of the third aspect, antenna configuration information comprises at least one of a phase shift and an amplitude for each of a plurality of antenna elements of the respective IRS.

In an implementation form of the third aspect, second channel estimation information comprises a channel quality indicator for each of a plurality of spatially multiplexed streams supported by the channel.

In an implementation form of the third aspect, the second channel estimation information is based on one or more secondary RS, which are different than the one or more RS transmitted from the second communication device to the first communication device.

In an implementation form of the third aspect, the method is performed by the first communication device.

In an implementation form of the third aspect, the first communication device is a network device, for example, a TRP; and/or the second communication device is a terminal device, for example, UE. The method of the third aspect may be performed by the processing device of the first aspect, and may achieve all advantages of the processing device of the first aspect.

A fourth aspect of this disclosure provides a method for improving a spatial multiplexing capability of a link between a first communication device and a second communication device, the method comprising: receiving, from the first communication device, IRS information indicating a number of IRSs selected from a set of IRSs available in the communication environment of the first and the second communication device, and reference signal, RS, information indicating one or more RS; and for each respective IRS in the subset of IRSs, the method further comprising: providing, to the first communication device, first and second channel estimation information, or only the second channel estimation information, for a channel including the link between the first and the second communication device and an additional link between the first and the second communication device via the respective IRS.

In an implementation form of the fourth aspect, the first and/or the second channel estimation information is based on respectively one or more primary and/or secondary RS transmitted from the first communication device to the second communication device.

In an implementation form of the fourth aspect, the method further comprises: receiving, from the first communication device, RS information indicating one or more RS; and if providing only the second channel estimation information to the first communication device: sending, for each respective IRS in the subset of IRSs, the one or more primary RS to the first communication device.

In an implementation form of the fourth aspect, the method further comprises providing position information and antenna array information of the second communication device to the first communication device.

In an implementation form of the fourth aspect, the method is performed by the second communication device.

The method of the fourth aspect may be performed by the processing device of the second aspect, and may achieve all advantages of the processing device of the second aspect. A fifth aspect of this disclosure provides a computer program comprising instructions which, when the program is executed by a processing device, for instance of the first or second aspect, respectively, causes the processing device to perform the method according to the third aspect or the fourth aspect or any implementation form thereof.

According to the above aspects and implementation forms, this disclosure proposes preselecting a subset of IRSs (from the total set of IRSs available in the communication environment of the two communication devices) for channel training. The pre-selection is based on the position information of the second communication device (e.g., a UE) and its antenna array information, as well as the IRS’ position information and their antenna array information. Associated with this, the disclosure also proposes the related signaling for setting up the training and estimation of the IRS augmented channels for the selected subset of IRSs, and finally for selecting the certain IRS for further communication between the two communication devices. The certain IRS may be selected to maximize the data rate between the two communication devices.

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

BRIEF DESCRIPTION OF DRAWINGS

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

FIG. 1 shows an indoor setup, in which many IRSs are mounted to walls, and many machines (UEs) are provided that experience a LOS link to a TRP or BS at least with a high probability. FIG. 2 shows an outdoor cellular setup, in which many IRSs are mounted on buildings, and wherein there is a high LOS link probability between a UE and a TRP due to shorter distances.

FIG. 3 shows a processing device according to an embodiment of this disclosure.

FIG. 4 shows a processing device according to an embodiment of this disclosure.

FIG. 5 illustrates a pre-selection of a subset of IRSs by a processing device according to an embodiment of this disclosure, in an exemplary indoor setup.

FIG. 6 shows a flow chart of an algorithm for selecting a subset of IRSs performed by a processing device according to an embodiment of this disclosure.

FIG. 7 shows a signaling diagram between communication devices (including processing devices) according to embodiments of this disclosure.

FIG. 8 shows a signaling diagram between communication devices (including processing devices) according to embodiments of this disclosure.

FIG. 9 shows a signaling diagram between communication devices (including processing devices) according to embodiments of this disclosure.

FIG. 10 shows a method according to an embodiment of this disclosure.

FIG. 11 shows a method according to an embodiment of this disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 shows a processing device 300 according to an embodiment of this disclosure. The processing device 300 may be used for improving a spatial multiplexing capability of a link between a first communication device 301 (e.g., a TRP) and a second communication device 302 (e.g., a UE). The processing device 300 may be the first communication device 301, or may be implemented in first communication device 301, or may at least communicate with the first communication device 301.

The processing device 300 is configured to select a subset of IRSs 303 from a set of IRSs available in a communication environment of the first and the second communication device 301 and 302. The subset of IRSs is selected based on position information 304 and antenna array information 305 of the second communication device 302 and of each IRS 303 in the set ofIRSs.

The IRSs 303 of the subset of IRSs may be selected based on their (and the second communication device’s) number of antennas, antenna pattern, antenna layout, and/or an antenna spacing. As an example, a plurality of IRSs 303 having the highest numbers of antennas and/or with largest antenna spacing may be selected. Further, the IRSs 303 of the subset of IRSs may also or additionally be selected based on their (and the second communication device’s) location and orientation in the communication environment of the first and the second communication device 301 and 302. For instance, a plurality of IRSs 303 that are closest to the first communication device 301 and/or are oriented optimally with respect to the first and/or the second communication device 301 and 302 may be selected. In this way, the subset of IRSs may be selected such that the IRSs 303 of the subset result in higher achievable rates than the other available IRSs 303 that are not selected for the subset of IRSs. More details of how the subset of IRSs may be selected are described below with respect to FIG. 6.

The processing device 300 is further configured, for each respective IRS 303 in the subset of IRSs, to obtain first channel estimation information 306 for a channel (IRS augmented channel) including the direct link 307 between the first and the second communication device 301 and 302 and an additional link 308 from the first to the second communication device 301 and 302 via the respective IRS 303. In other words, the first channel estimation information 306 is obtained for the IRS augmented channel when using the respective IRS 303.

The processing device 300 is further configured, for each respective IRS 303 in the subset of IRSs, to provide antenna configuration information 309 to the respective IRS 303. The antenna configuration information 309 is based on the first channel estimation information 306 obtained for the respective IRS 303, i.e., for the respective IRS augmented channel. The antenna configuration information 309 may comprise at least one of a phase shift and an amplitude for each of a plurality of antenna elements of the respective IRS 303.

FIG. 4 shows another processing device 400 according to an embodiment of this disclosure. The processing device 400 may be used for improving a spatial multiplexing capability of the link between the first communication device 301 and the second communication device 302. The processing device 400 may be the second communication device 302, or may be implemented in the second communication device 302, or may at least communicate with the second communication device 302.

The processing device 400 is configured to receive, from the first communication device 301, IRS information 401 indicating a number of IRSs 303 selected from a set of IRSs available in the communication environment of the first and the second communication device 301 and 302. The number of IRSs 303 may be closely related (or identical to) the IRSs 303 of the subset of IRSs selected by the processing device 300 (as described above with regard to FIG. 3). Along with the IRS information 401, the processing device 400 may also receive RS information indicating one or more RS from the first communication device 301.

Further, the processing device 400 is configured, for each respective IRS 303 of the number of IRSs (e.g., for each IRS 303 in the subset of IRSs selected by the processing device 300), to provide, to the first communication device 301, the first channel estimation information 306 and second channel estimation information 402, or only the second channel estimation information 402, for a channel including the direct link 307 between the first and the second communication device 301 and 302 and the additional link 308 between the first and the second communication device 301 and 302 via the respective IRS 303. That is, the processing device 400 is configured to obtain the first channel estimation information 306 and/or the second channel estimation information 402 for the IRS augmented channel using the respective IRS 303, and may feed this back to the first communication device 301.

At least one of the processing device 300 and the processing device 400 may comprise a processor or processing circuitry (not shown) configured to perform, conduct or initiate the various operations of the processing device 300 and/or the processing device 400 described herein. The processing circuitry may comprise hardware and/or the processing circuitry may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise components such as applicationspecific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multi-purpose processors.

At least one of the processing device 300 and the processing device 400 may further comprise memory circuitry, which stores one or more instruction(s) that can be executed by the processor or by the processing circuitry, in particular under control of the software. For instance, the memory circuitry may comprise a non-transitory storage medium storing executable software code which, when executed by the processor or the processing circuitry, causes the various operations of the processing device 300 and/or the processing device 400 to be performed. In one embodiment, the processing circuitry comprises one or more processors and a non- transitory memory connected to the one or more processors. The non-transitory memory may carry executable program code which, when executed by the one or more processors, causes the processing device 300 and/or the processing device 400 to perform, conduct or initiate the operations or methods described herein.

As can be understood from the above description, in order to reduce the signaling overhead that would be associated with training and estimating all possible IRS augmented channels (i.e., for each available IRS 303) in the communication environment of the first and second communication device 301 and 302, the present disclosure proposes a procedure that judiciously selects only the subset of IRSs for training. This training may include obtaining the first channel estimation information 306 and obtaining the second channel estimation information 402 (after providing the antenna configuration information 309 to the respective IRS 303 of the subset).

The procedures of the present disclosure may be based on the two following assumptions: firstly, a pure LOS link between the first and the second communication device 301 and 302, and, secondly, a noise plus interference vector at the second communication device 302 having uncorrelated spatial entries. In this case, the achievable rate of any IRS augmented channel between the first and the second communication device 301 and 302 is affected by the position and/or orientation of the IRS 303 relative to the two communication devices 301 and 302, i.e., it depends on the position information 304. Moreover, under these assumptions, the IRS augmented channels can be calculated at the first communication device 301 based only on the position information 304 and the antenna array information 305 of the two communication devices 301 and 302, and of the available IRSs 303, and hence, no training and estimation is required for selecting the subset.

The IRS’ position information 304 and antenna array information 305 can be communicated to the first communication device 301 by the network after IRS installation. Alternatively, the IRSs 303 may each have a controller connected to the network. Hence, any IRS 303 could also signal its position information 304 and antenna array information 305 to the first communication device 301. The antenna array information 305 of the second communication device 302 can be communicated in a similar manner, i.e., either by the network or by the second communication device 302 itself. The position information 304 of the second communication device 302 can be obtained at the first communication device 301 using, e.g., a standard 5G positioning procedure (where the communication devices 301 and 302 may be TRP and UE, respectively). All this information 304 and 305 can be obtained easily at the first communication device 301, and may be considered as a-priori information.

Based on this a-priori information, the processing device 300 may select the subset of IRSs. In particular, the processing device 300 may calculate an IRS augmented channel for each available IRS in the communication environment of the communication devices 301 and 302, and may calculate an achievable rate for each IRS augmented channel. The subset of IRSs may then be formed by selecting the IRSs 303 resulting in the highest achievable rates.

FIG. 5 illustrates an example of a selected subset of IRSs in an indoor setup as described with respect to FIG. 1. Here, the processing device 300 has exemplarily selected two IRS 303 from all available IRSs for the subset. Two IRS augmented channels may accordingly be formed based, respectively, on each of the selected IRS 303. The two IRSs are selected for a certain machine (UE) in the communication environment, i.e., a second communication device 302 under consideration. For any other machine, other IRSs may likely be selected for forming the subset. The selected IRSs, if chosen based on the above-described assumptions, would result in higher achievable rates compared to the rest of the IRSs 303 that are not selected. In FIG. 5 this is the case, for example, because the selected IRSs 303 are located approximately at equal distances to both the TRP, i.e., the first communication device 301, and the machine under consideration.

An example of how the IRS augmented channels for the available IRSs may be calculated, in order to select the subset of IRSs from the available IRSs, is shown in FIG. 6. In particular, FIG. 6 shows how the IRS augmented channels may be calculated based on the a-priori information and under the above-mentioned LOS assumption. FIG. 6 shows in this respect a flow chart of an algorithm flow that may be performed by the processing device 300. Here the processing device 300 is exemplarily included in the first communication device 301 (TRP, in this exemplary case). The algorithm is repeated for every IRS 303. The algorithm calculates the IRS augmented channel for each respective IRS 303, and ultimately the achievable rate for the respective IRS 303. It can be seen that for a direct link between the first communication device 301 and the respective IRS 303, an angle of arrival (Ao A) and an angle of departure (AoD) may be calculated based on the position information 304 and antenna array orientation (which may be part of the antenna array information 305, and indicates how the antenna array is oriented in the communication environment) of the respective IRS 303 and the first communication device 301. Then, a LOS channel for that link between the first communication device 301 and the respective IRS 303 may be calculated based on the AoA and AoD and based further on antenna array configuration (which may be a part of the antenna array information 305, and indicates e.g. the number of antennas or antenna spacing) of the respective IRS 303 and the first communication device 301. The same calculations of AoA, AoD, and channel may be done for the direct link between the respective IRS 303 and second communication device 302 (of course based on the corresponding position information 304 and antenna array information 305), Notably, the direct link between the first communication device 301 and the respective IRS 303 and the direct link between the respective IRS 303 and second communication device 302 (sublinks) together form the indirect link between the first communication device 301 and the second communication device 302 via the respective IRS 303. The same calculations are also done for the direct link between the first communication device 301 and the second communication device 302 (again based on the corresponding position information 304 and antenna array information 305).

Once all the channels, particularly the channels between the first communication device 301 and IRS 303 and between the IRS 303 and the second communication device 302, are calculated by the first communication device 301 for each respective IRS 303, the first communication device 301 can calculate the achievable rate for each IRS augmented channel. For instance, the first communication device may calculate, for each respective IRS 303, the antenna configuration information 309 that maximizes the rank of the IRS augmented channel for the respective IRS. Based on the calculated antenna configuration information 309, e.g., including phase shifts and/or amplitudes for different antenna elements of the respective IRS 303, a spatial precoder of the first communication device 301 can be calculated for maximizing the achievable rate of the IRS augmented channel for the respective IRS 303. Thereby, the achievable rate for each respective IRS 303 in the system can be obtained.

In a subsequent step, the first communication device 301 can then select the subset of IRSs including those IRSs 303 that yield the largest achievable rates. For instance, a certain predetermined number of IRSs 303 that achieve the highest rates, or all IRSs 303 resulting in rates above a certain threshold rate. This subset of IRSs is chosen as a basis for a subsequent channel training phase. The channel training phase is beneficial, as in practice there may always be some non-LOS components additional to the LOS components of each link, which may affect the actual channel conditions. Also, the interference vector at the second communication device 302 may have spatially correlated entries. The channel training phase may include the transmission of RSs and performing channel estimation. The channel training phase is, however, only performed for the subset not the complete set of available IRSs 303. Thus, much less overhead is generated. For selecting the subset according to the above, no RSs or channel estimation are needed, so no overhead is produced.

Based on the above, a complete example procedure of this disclosure can be described as follows, wherein the procedure including the training and signaling steps. In the exemplary procedure, it is again assumed that the first communication device 301 (e.g., TRP or BS) is or includes the processing device 300, and that the second communication device 302 (e.g., UE) is or includes the processing device 400.

1. IRS subset selection: Based on the position information 304 and the antenna array information 305 of the second communication device 302 and of each IRS 303 in the communication environment, the first communication device 301 selects a subset of IRSs for potential communication with a given second communication device 302. The selection can be done as described above. The first communication device 301 then informs the second communication device 302 of the number of IRSs 303 that needs to be probed, potentially together with the corresponding RS to be used. The first communication device 300 also configures the chosen IRSs 303 of the subset of IRSs for channel estimation, by informing these IRSs 303 of configuration information (e.g., sets of phase shifts) to be used.

2. First training stage: For each respective IRS 303 of the IRSs 303 in the subset of IRSs, an IRS augmented channel (i.e., comprising the direct link between the first and the second communication device 301 and 302 plus the indirect link between the first and second communication device 301 and 302 via the respective IRS 303) is estimated by the first communication device 301 in the UL based on RS 702 transmitted by the second communication device 302. The result of this estimation is the first channel estimation information 306.

3. Processing and signaling: Based on the estimated channels, i.e., the first channel estimation information 306, the first communication device 301 performs an optimization to find the most appropriate antenna configuration information 309 (e.g., phase shifts and amplitudes for the antenna elements) for each respective IRS of the subset of IRSs 303 for data communication. The first communication device 301 informs the selected IRSs 303 to configure, e.g., the phase shifts and amplitudes for their antenna elements correspondingly.

4. Second training stage: For each IRS 303 of the IRSs 303 in the chosen subset, the IRS augmented channel is estimated, wherein an antenna configuration of each IRS 303 is set according to the antenna configuration information 309 (e.g., phase shifts) and a precoder of the first communication device 301 is appropriately chosen. The second communication device 302 may, in particular, calculate second channel estimation information 402 (e.g., a channel quality indicator (CQI) of each spatially multiplexed stream) and feeds this information 402 back to the first communication device 301. Note that in general a different RS configuration may be required here than in step 2 (for instance, the RS length for channel estimation is in general longer than the one required for CQI estimation).

5. Final choice: Based on the feedback of the second channel estimation information 402 from the second communication device 302, the first communication device 301 chooses a certain IRS 303 from the subset of IRSs, for data communication with the concerned second communication device 302, and then informs the certain IRS 303 to keep its antenna configuration and informs the remaining IRSs 303 in the subset to revoke their previously obtained antenna configuration, or informs them to be turned off.

Notably, in a practical setup (e.g., an industry 4.0 smart factory indoor setup or an outdoor cellular scenario), there may be other communication devices, e.g., other first communication devices (TPRs) and IRSs potentially serving other second communication devices (UEs) that may cause interference to the concerned second communication device 302. Therefore, step 4 is beneficial, since the first communication device 301 is unaware of the interference at the concerned second communication device 302. The estimation of the interference may implicitly be done at the second communication device 302 by calculating the second channel estimation information 402 (e.g., CQI) per stream and feeding this information 402 back to the serving first communication device 301.

The disclosure may moreover be oriented towards a multiuser system, where different second communication devices (e.g., UEs) may have different priorities and may be unaware of each other’s priorities. Therefore, the first communication device 301 may beneficially make the final decision based on the collected information from all the second communication devices. In other words, in a multiuser system, the second communication device 302 cannot choose the desired IRS 303 itself. For this reason, the feedback in step 4 and the details of step 5 are beneficial.

Using the above described exemplary procedure enables a significant reduction of the training and signaling overhead, which is associated with choosing one IRS 303 out of many available IRSs 303, in order to maximize the achievable rate in a wireless communication system.

In the following an exemplary specific embodiment for a system with three available IRS 303, two out of which are selected for training (i.e., as the subset of IRSs), is described. Reference is made to FIG. 7, 8 and 9. Again, it is assumed that the first communication device 301, here a TRP 301, includes or is the processing device 300. Further, that the second communication device 302, here a UE 302, includes or is the processing device 400.

In an initial signaling step shown in FIG. 7, the IRS’ and UE’s position information 304 and antenna array information 305 are conveyed to the TRP 301, for instance, from a network device 701 or higher layers or from the IRSs 303 and the UEs 302 themselves (to be performed for every IRS 303 and UE 302 in the system).

After that, the complete procedure for configuring the IRS subset and finally selecting a certain IRS 303 from the subset for communication with a certain UE 302 is illustrated in FIG. 8.

First, IRS information 401 indicating a number of IRSs 303 selected from a set of IRSs available in the communication environment of the TRP 301 and UE 302 is provided from the TRP 301 to the UE 302. Along with the IRS information 401, also RS information indicating one or more RS 802 may be provided from the TRP 301 to the UE 302. The IRSs 303 in the subset may then be provided with configuration information 801, for instance, including phase shifts for their antenna elements, by the TRP 301.

The one or more RS 802 are then transmitted from the UE 302 to the TRP 301. The TRP 301 can then estimate the channel based on the one or more RS 802, to obtain the first channel estimation information 306. Then, the TRP 301 provides the antenna configuration information 309 to each respective IRS 303 in the subset of IRSs, wherein the antenna configuration information 309 is based on the first channel estimation information 306 obtained for the respective IRS 303.

Then, the TRP 301 may send one or more secondary RS 803, which are different than the one or more RS 802 transmitted from the UE 302 to the TRP 301, to the UE 302. The UE 302 may then provide the second channel estimation information 402 to the TRP 301, wherein the second channel estimation information 402 is based on the secondary RS 803 transmitted from the TRP

301 to the UE 302.

Then, the TRP 301 selects a certain IRS 303 (here the IRS 2) from the subset of IRSs for further communication between the TRP 301 and the UE 302, based on the second channel estimation information 402 for each respective IRS 303 in the subset of IRSs. Finally, the TRP 301 provides, to the certain IRS 303 selected from the subset of IRSs, an indication 805 to keep the previously provided antenna configuration information 309, and/or provides, to each other IRS 303 not selected from the subset of IRSs, an indication 804 to revoke the previously provided antenna configuration information 309.

FIG. 9 shows an alternative to FIG. 8, wherein instead of sending RS 802 from the UE 302 to the TRP 301 (as in FIG. 8), other RS 903 can be sent from the TRP 301 to the UE 302. The UE

302 may obtain the first channel estimation information 306 in this case based on the one or more RS 903. The UE 302 can then feed the first channel estimation information 306 back to the TRP 301, which may then proceed with sending the antenna configuration information 309 to the respective IRS 303 (as in FIG. 8). All further steps are as in FIG. 8 and thus not described again. FIG. 10 shows a method 1000 according to an embodiment of this disclosure. The method 1000 is for improving a spatial multiplexing capability of a link between the first communication device 301 and a second communication device 302. The method 1000 may be performed by the processing device 300 or by the first communication device 301.

The method comprises a step 1001 of selecting a subset of IRSs 303 from a set of IRSs available in a communication environment of the first and the second communication device 301 and 302. The subset of IRSs is selected based on position information 304 and antenna array information 305 of both the second communication device 302 and of each IRS 303 in the set of IRSs. Then, the method 1000 further comprises, for each respective IRS 303 in the subset of IRSs: a step 1002 of obtaining first channel estimation information 306 for a channel including the link 307 between the first and the second communication device 301 and 302, and an additional link 308 between the first and the second communication device 301 and 302 via the respective IRS 303. Further, also a step 1003 of providing antenna configuration information 309 to the respective IRS 303, wherein the antenna configuration information 309 is based on the first channel estimation information 306 obtained for the respective IRS 303.

FIG. 11 shows a method 1100 according to an embodiment of this disclosure. The method 1100 is for improving a spatial multiplexing capability of a link between the first communication device 301 and the second communication device 302. The method may be performed by the processing device 400 or the second communication device 302.

The method 1100 comprises a step 1101 of receiving, from the first communication device

301, IRS information 401 indicating a number of IRSs 303 selected from a set of IRSs available in the communication environment of the first and the second communication device 301 and

302. Further, the method 1100 comprises, for each respective IRS 303 of the number of IRSs: a step 1102 of providing, to the first communication device 301, first and second channel estimation information 306 and 402, or only the second channel estimation information 402, for a channel including the link 307 between the first and the second communication device 301, 302, and an additional link 308 between the first and the second communication device 301 and 302 via the respective IRS 303.

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

Claims

1. A processing device (300) for improving a spatial multiplexing capability of a link between a first communication device (301) and a second communication device (302), the processing device (300) being configured to: select a subset of intelligent reflecting surfaces, IRSs, (303) from a set of IRSs available in a communication environment of the first and the second communication device (301, 302), wherein the subset of IRSs is selected based on position information (304) and antenna array information (305) of both the second communication device (302) and each IRS (303) in the set of IRSs; and for each respective IRS (303) in the subset of IRSs, the processing device (300) being further configured to: obtain first channel estimation information (306) for a channel including the link (307) between the first and the second communication device (301, 302) and an additional link (308) between the first and the second communication device (301, 302) via the respective IRS (303); and provide antenna configuration information (309) to the respective IRS (303), wherein the antenna configuration information (309) is based on the first channel estimation information (306) obtained for the respective IRS (303).

2. The processing device (300) according to claim 1, wherein the processing device(300) is configured to obtain the first channel estimation information (306) via:

- estimating the channel; or

- receiving the first channel estimation information (306) from the second communication device (302).

3. The processing device (300) according to claim 2, wherein the processing device (300) is configured to estimate the channel based on one or more reference signals, RS, (802) transmitted from the second communication device (302) to the first communication device (301).

25

4. The processing device (303) according to one of the claims 1 to 3, further configured to, after providing the antenna configuration information (309) to the respective IRS (303): receive, from the second communication device (302), second channel estimation information (402) for the channel estimated for the respective IRS (303).

5. The processing device (300) according to claim 4, further configured to: select a certain IRS (303) from the subset of IRSs for further communication between the first and the second communication device (301, 302), wherein the certain IRS (303) is selected based on the second channel estimation (402) information for each respective IRS (303) in the subset of IRSs.

6. The processing device (300) according to one of the claims 1 to 5, further configured to: provide, to the certain IRS (303) selected from the subset of IRSs, an indication (805) to keep the previously provided antenna configuration information (309); and/or provide, to each IRS (303) not selected from the subset of IRSs, an indication (804) to revoke the previously provided antenna configuration information (309).

7. The processing device (300) according to one of the claims 1 to 6, further configured to obtain the position information (304) and antenna array information (305) of both the second communication device (302) and each IRS (303) in the set of IRSs from at least one of: a network device (701), one or more IRSs (303) in the set of IRSs, and the second communication device (302).

8. The processing device (300) according to one of the claims 1 to 7, further configured to provide, to the second communication device (302), IRS information (401) indicating the number of IRSs (303) selected from the set of IRSs.

9. The processing device (300) according to the claims 3 and 8, further configured to provide, to the second communication device (302) along with the IRS information (401), RS information indicating the one or more RS (802).

10. The processing device (300) according to one of the claims 1 to 9, wherein antenna array information (305) comprises at least one of a number of antennas, an antenna pattern, an antenna layout, and an antenna spacing.

11. The processing device (300) according to one of the claims 1 to 10, wherein position information (304) comprises at least one of a location and an orientation in the communication environment of the first and the second communication device (301, 302).

12. The processing device (300) according to one of the claims 1 to 11, wherein antenna configuration information (309) comprises at least one of a phase shift and an amplitude for each of a plurality of antenna elements of the respective IRS (303).

13. The processing device (300) according to one of the claims 1 to 12, wherein second channel estimation information (402) comprises a channel quality indicator for each of a plurality of spatially multiplexed streams supported by the channel.

14. The processing device (300) according to one of the claims 4 to 11, wherein the second channel estimation information (402) is based on one or more secondary RS (803), which are different than the one or more RS (802) transmitted from the second communication device (302) to the first communication device (301).

15. The processing device (300) according to one of the claims 1 to 14, wherein the processing device (300) is or is included in the first communication device (301).

16. The processing device (300) according to one of the claims 1 to 15, wherein: the first communication device (301) is a network device, for example, a transmit- receive-point; and/or the second communication device (302) is a terminal device, for example, user equipment.

17. A processing device (400) for improving a spatial multiplexing capability of a link between a first communication device (301) and a second communication device (302), the processing device (400) being configured to: receive, from the first communication device (302), IRS information (401) indicating a number of intelligent reflecting surfaces, IRSs, (303) selected from a set of IRSs available in the communication environment of the first and the second communication device (301, 302); and for each respective IRS (303) of the number of IRSs, the processing device (400) being further configured to: provide, to the first communication device (301), first and second channel estimation information (306, 402), or only the second channel estimation information (402), for a channel including the link (307) between the first and the second communication device (301, 302) and an additional link (308) between the first and the second communication device (301, 302) via the respective IRS (303).

18. The processing device (400) according to claim 17, wherein the first and/or the second channel estimation information (306, 402) is based on respectively one or more primary and/or secondary reference signals, RS, (803) transmitted from the first communication device (301) to the second communication device (302).

19. The processing device (400) according to claim 17 or 18, further configured to: receive, from the first communication device (301), RS information indicating one or more RS (802); and if providing only the second channel estimation information (402) to the first communication device (301): send, for each respective IRS (303) of the number of IRSs, the one or more primary RS (802) to the first communication device (301).

20. The processing device (400) according to one of the claims 17 to 19, further configured to: provide position information (304) and antenna array information (305) of the second communication device (302) to the first communication device (301).

21. The processing device (400) according to one of the claims 17 to 20, wherein the processing device (400) is or is included in the second communication device (302).

28

22. A method (1000) for improving a spatial multiplexing capability of a link between a first communication device (301) and a second communication device (302), the method (1000) comprising: selecting (801) a subset of intelligent reflecting surfaces, IRSs, (303) from a set of IRSs available in a communication environment of the first and the second communication device (301, 302), wherein the subset of IRSs is selected based on position information (304) and antenna array information (305) of both the second communication device (302) and of each IRS (303) in the set of IRSs; and for each respective IRS (303) in the subset of IRSs, the method (800) further comprising: obtaining (802) first channel estimation information (306) for a channel including the link (307) between the first and the second communication device (301, 302) and an additional link (308) between the first and the second communication device (301, 302) via the respective IRS (303); and providing (803) antenna configuration information (309) to the respective IRS (303), wherein the antenna configuration information (309) is based on the first channel estimation information (306) obtained for the respective IRS (303).

23. A method (900) for improving a spatial multiplexing capability of a link between a first communication device (301) and a second communication device (302), the method (900) comprising: receiving (901), from the first communication device (302), IRS information (401) indicating a number of intelligent reflecting surfaces, IRSs, (303) selected from a set of IRSs available in the communication environment of the first and the second communication device (301, 302); and for each respective IRS (303) of the number of IRSs, the method (900) further comprising: providing (902), to the first communication device (301), first and second channel estimation information (306, 402), or only the second channel estimation information (402), for a channel including the link (307) between the first and the second communication device (301, 302) and an additional link (308) between the first and the second communication device (301, 302) via the respective IRS (303).

29

24. A computer program comprising instructions which, when the program is executed by a processing device (300, 400), causes the processing device (300, 400) to perform the method (1000, 900) according to claim 22 or 23.

30