Technical Field

Examples of the invention relates to a reflective intelligent surface arrangement for encoding information bits. Furthermore, the invention also relates to a network access node, a client device, corresponding methods and a computer program.

Background

Reflective intelligent surface (RIS) has been introduced as an enabling technology to engineer the radio signal propagation in wireless networks. Specifically, interdisciplinary development of meta-materials, electromagnetics, and wireless communications introduces a revolutionary technique which is smartly tuning the signal reflection via a large number of low-cost passive reflecting elements. The RIS technology is therefore capable of dynamically altering wireless channels to enhance the communication performance.

A RIS arrangement or device is a combination of an array and a controller. The array is composed of a large number of passive elements, a.k.a. metasurfaces, which reflect electromagnetic signals in a desired manner so as to alter or reconfigure the wireless environment. Since the elements of a RIS arrangement do not introduce additional noise component in the system, they are classified as passive elements. The RIS controller is capable of controlling each metasurface element of the array. Current implementation of metasurface includes conventional reflect-arrays, liquid crystal surfaces, and software-defined metasurfaces. Nowadays, different RIS implementations used for coverage improvement, interference coordination, assisting beamforming procedure have been proposed.

Summary

An objective of examples of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.

The above and further objectives are solved by the subject matter of the independent claims. Further examples of the invention can be found in the dependent claims.

According to a first aspect of the invention, the above mentioned and other objectives are achieved with a reflective intelligent surface, RIS, arrangement for a communication system, the RIS arrangement comprising: an array of passive reflective elements configured to reflect an incoming signal; and a controller configured to control the array of passive reflective elements to change a reflection delay or a reflection direction for the incoming signal, the controller further being configured to obtain one or more information bits; and encode the one or more information bits into the incoming signal by controlling a reflection delay or a reflection direction for the incoming signal based on the one or more information bits.

An advantage of the RIS arrangement according to the first aspect is that it enables the transmission of extra information in the communication system without occupying extra resources such as time, frequency, transmission power, etc. For example, a gNB may transmit extra information to a UE when RIS is considered by utilizing the flexibility of the RIS arrangement in controlling the channel propagation properties. Hence, a new functionality of the RIS arrangement is provided that has not been considered before.

In an implementation form of a RIS arrangement according to the first aspect, encoding the one or more information bits by controlling the reflection delay is based on controlling a duration of the reflection delay.

An advantage with this implementation form is that the information bits may be encoded without changing the spatial properties of the incoming signal which means that no added complexity has to be implemented in the transmitter or the receiver.

In an implementation form of a RIS arrangement according to the first aspect, the incoming signal carries a set of OFDM symbols, and wherein controlling the duration of the reflection delay comprises: controlling the duration of the reflection delay in a cyclic prefix of a OFDM symbol in the set of OFDM symbols.

An advantage with this implementation form is that by encoding the information bits in the cyclic prefix of the OFDM symbol inter-symbol interference can be avoided or minimized.

In an implementation form of a RIS arrangement according to the first aspect, encoding the one or more information bits comprises: controlling the duration of the reflection delay in the cyclic prefix of the OFDM symbol in relation to a duration of a reflection delay in a cyclic prefix of a previous OFDM symbol in the set of OFDM symbols; controlling the duration of the reflection delay in the cyclic prefix of the OFDM symbol in relation to a duration of a reflection delay in a cyclic prefix of a first OFDM symbol in the set of OFDM symbols; or controlling the duration of the reflection delay in the cyclic prefix of the OFDM symbol in relation to a threshold value.

An advantage with this implementation form is that the present solution can be implemented in a robust way in mobile scenarios.

In an implementation form of a RIS arrangement according to the first aspect, encoding the one or more information bits by controlling the reflection direction is based on controlling an azimuth reflection angle and/or an elevation reflection angle of the reflection direction.

An advantage with this implementation form is that the encoding of the information bits can be implemented with shorter symbol duration compared to encoding by controlling the reflection delay which e.g., implies higher encoding frequency.

In an implementation form of a RIS arrangement according to the first aspect, encoding the one or more information bits comprises: controlling the azimuth reflection angle and the elevation reflection angle based on a two-dimensional codebook grid given by the azimuth reflection angle and the elevation reflection angle.

An advantage with this implementation form is that encoding can be performed in two angular dimensions.

In an implementation form of a RIS arrangement according to the first aspect, the one or more information bits are associated with control information.

In an implementation form of a RIS arrangement according to the first aspect, the RIS arrangement is further configured to receive a RIS control message from a network access node, the RIS control message indicating one or more encoding control parameters for controlling the array of passive reflective elements; and wherein the controller is configured to control the array of passive reflective elements for encoding the one or more information bits further based on the RIS control message. An advantage with this implementation form is that the RIS control message makes it possible for the network to control the encoding at the RIS arrangement.

According to a second aspect of the invention, the above mentioned and other objectives are achieved with a network access node being configured to: transmit a RIS control message to a RIS arrangement, the RIS control message indicating one or more encoding control parameters for controlling an array of passive reflective elements for encoding one or more information bits.

An advantage of the network access node according to the second aspect is that the network access node can control the RIS arrangement for encoding one or more information bits.

In an implementation form of a network access node according to the second aspect, the network access node further being configured to transmit a configuration message to a client device, the configuration message indicating a RIS decoding configuration for the client device.

An advantage with this implementation form is that the client device is provided with decoding information so as to be able to decode correctly.

In an implementation form of a network access node according to the second aspect, the configuration message further indicates aperiodic decoding or semi-persistent decoding.

In an implementation form of a network access node according to the second aspect, the network access node further being configured to transmit an activation/deactivation message to the client device, the activation/ deactivation message indicating activation/deactivation of the RIS decoding configuration for the client device.

An advantage with this implementation form is that the network can control the activation and deactivation of RIS encoding/decoding. Hence, the network is provided with an activation/deactivation mechanism thereby, e.g., adapting RIS encoding to channel conditions and/or network conditions in the communication system.

In an implementation form of a network access node according to the second aspect, the network access node further being configured to receive a capability message from the client device previous to transmitting the configuration message, the capability message indicating a RIS decoding capability of the client device; and determine the configuration message based on the capability message.

An advantage with this implementation form is that the network is informed about the decoding capabilities of the client device so as to adapt the RIS encoding to such decoding capabilities of the client device.

In an implementation form of a network access node according to the second aspect, the network access node further being configured to transmit a capability enquiry message to the client device previous to receiving the capability control message, the capability enquiry message indicating a request for the RIS decoding capability of the client device.

An advantage with this implementation form is that the client device is triggered to inform the network about its decoding capabilities for improved encoding.

According to a third aspect of the invention, the above mentioned and other objectives are achieved with a client device being configured to receive a signal from a RIS arrangement, the signal comprising one or more encoded information bits; and decode the signal to derive the one or more encoded information bits based on determining a RIS reflection delay or a RIS reflection direction of the signal.

An advantage of the client device according to the third aspect is that is that it enables the reception of extra information in the communication system without occupying extra resources such as time, frequency, transmission power, etc.

In an implementation form of a client device according to the third aspect, the one or more information bits are encoded based on a duration of the RIS reflection delay, and wherein the client device is configured to decode the signal to derive the one or more encoded information bits based on determining the duration of the RIS reflection delay. An advantage with this implementation form is that the information bits may be encoded/decoded without changing the spatial properties of the incoming signal which means that no added complexity has to be implemented in the transmitter or the receiver.

In an implementation form of a client device according to the third aspect, the signal carries a set of OFDM symbols, and wherein the one or more information bits are encoded based on the duration of the RIS reflection delay in a cyclic prefix of a OFDM symbol in the set of

OFDM symbols.

An advantage with this implementation form is that by encoding the information bits in the cyclic prefix of the OFDM symbol inter-symbol interference can be avoided or minimized.

In an implementation form of a client device according to the third aspect, the one or more information bits are encoded based on: the duration of the RIS reflection delay in the cyclic prefix of the OFDM symbol in relation to a duration of a RIS reflection delay in a cyclic prefix of a previous OFDM symbol in the set of OFDM symbols; the duration of the RIS reflection delay in the cyclic prefix of the OFDM symbol in relation to a duration of a RIS reflection delay in a cyclic prefix of a first OFDM symbol in the set of OFDM symbols; or the duration of the RIS reflection delay in the cyclic prefix of the OFDM symbol in relation to a threshold value.

An advantage with this implementation form is that the present solution can be implemented in a robust way in mobile scenarios.

In an implementation form of a client device according to the third aspect, the one or more information bits are encoded based on an azimuth reflection angle and/or an elevation reflection angle of the RIS reflection direction, and wherein the client device is configured to decode the signal to derive the one or more encoded information bits based on determining the azimuth reflection angle and/or the elevation reflection angle.

An advantage with this implementation form is that the encoding of the information bits can be implemented with shorter symbol duration compared to encoding by controlling the reflection delay which e.g., implies higher encoding/decoding frequency. In an implementation form of a client device according to the third aspect, the one or more information bits are encoded based on the azimuth reflection angle and the elevation reflection angle in a two-dimensional codebook grid given by the azimuth reflection angle and the elevation reflection angle.

An advantage with this implementation form is that decoding can be performed in two angular dimensions.

In an implementation form of a client device according to the third aspect, the one or more information bits are associated with control information.

In an implementation form of a client device according to the third aspect, the client device further being configured to receive a configuration message from a network access node, the configuration message indicating a RIS decoding configuration for the client device; and decode the signal to derive the one or more encoded information bits further based on the RIS configuration message.

An advantage with this implementation form is that the client device is provided with decoding information so as to be able to decode correctly.

In an implementation form of a client device according to the third aspect, the configuration message further indicates aperiodic decoding or semi-persistent decoding; and the client device further being configured to decode the signal to derive the one or more encoded information bits based on aperiodic decoding or semi-persistent decoding.

In an implementation form of a client device according to the third aspect, the client device further being configured to receive an activation/deactivation message from the network access node, the activation/deactivation message indicating activation/deactivation of the RIS decoding configuration for the client device; and activate/deactivate the RIS decoding configuration for the client device based on the activation/deactivation message.

An advantage with this implementation form is that the network can control the activation and deactivation of RIS encoding/decoding at the client device. Hence, the network is provided with an activation/deactivation mechanism thereby, e.g., adapting RIS encoding to channel conditions and/or network conditions in the communication system.

In an implementation form of a client device according to the third aspect, the client device further being configured to transmit a capability message to the network access node previous to receiving the configuration message, the capability message indicating a RIS decoding capability of the client device.

An advantage with this implementation form is that the network is informed about the decoding capabilities of the client device so as to adapt the RIS encoding to such decoding capabilities of the client device.

In an implementation form of a client device according to the third aspect, the client device further being configured to receive a capability enquiry message from the network access node previous to transmitting the capability control message, the capability enquiry message indicating a request for the RIS decoding capability of the client device; and determine the RIS decoding capability of the client device based on the capability enquiry message.

An advantage with this implementation form is that the client device is triggered to inform the network about its decoding capabilities for improved encoding.

According to a fourth aspect of the invention, the above mentioned and other objectives are achieved with a method for a RIS arrangement comprising: an array of passive reflective elements configured to reflect an incoming signal; and a controller configured to control the array of passive reflective elements to change a reflection delay or a reflection direction for the incoming signal; the method comprising: obtaining one or more information bits; and encoding the one or more information bits into the incoming signal by controlling a reflection delay or a reflection direction for the incoming signal based on the one or more information bits.

The method according to the fourth aspect can be extended into implementation forms corresponding to the implementation forms of the RIS arrangement according to the first aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the RIS arrangement.

The advantages of the methods according to the fourth aspect are the same as those for the corresponding implementation forms of the RIS arrangement according to the first aspect.

According to a fifth aspect of the invention, the above mentioned and other objectives are achieved with a method for a network access node, the method comprising: transmitting a RIS control message to a RIS arrangement, the RIS control message indicating one or more encoding control parameters for controlling an array of passive reflective elements for encoding one or more information bits.

The method according to the fifth aspect can be extended into implementation forms corresponding to the implementation forms of the network access node according to the second aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the network access node.

The advantages of the methods according to the fifth aspect are the same as those for the corresponding implementation forms of the network access node according to the second aspect.

According to a sixth aspect of the invention, the above mentioned and other objectives are achieved with a method for a client device, the method comprising: receiving a signal from a RIS arrangement, the signal comprising one or more encoded information bits; and decoding the signal to derive the one or more encoded information bits based on determining a RIS reflection delay or a RIS reflection direction of the signal.

The method according to the sixth aspect can be extended into implementation forms corresponding to the implementation forms of the client device according to the third aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the client device.

The advantages of the methods according to the sixth aspect are the same as those for the corresponding implementation forms of the client device according to the third aspect. Examples of the invention also relates to a computer program, characterized in program code, which when run by at least one processor causes said at least one processor to execute any method according to examples of the invention. Further, examples of the invention also relate to a computer program product comprising a computer readable medium and said mentioned computer program, wherein said computer program is included in the computer readable medium, and comprises of one or more from the group: Read-Only Memory (ROM), Programmable ROM (PROM), Erasable PROM (EPROM), Flash memory, Electrically EPROM (EEPROM) and hard disk drive.

Further applications and advantages of examples of the invention will be apparent from the following detailed description.

Brief Description of the Drawings

The appended drawings are intended to clarify and explain different examples of the invention, in which:

- Fig. 1 shows a RIS arrangement according to an example of the invention;

- Fig. 2 shows a method for a RIS arrangement according to an example of the invention;

- Fig. 3 shows a network access node according to an example of the invention;

- Fig. 4 shows a method for a network access node according to an example of the invention;

- Fig. 5 shows a client device according to an example of the invention;

- Fig. 6 shows a method for a client device according to an example of the invention;

- Fig. 7 illustrates a communication system according to an example of the invention;

- Fig. 8 illustrates encoding by altering the reflection delay of an incoming signal according to an example of the invention;

- Fig. 9 illustrates encoding by altering a reflection angle of an incoming signal according to an example of the invention; and

- Fig. 10 shows a signaling diagram illustrating the interaction between different devices in a communication system according to an example of the invention.

Detailed Description

It is herein disclosed to use a RIS arrangement in order to provide what may be considered as an additional communication channel between a transmitter and a receiver in a communication system. By controlling the signal propagation between the transmitter and the receiver by means of an intermediate RIS arrangement one or more information bits can be encoded without occupying extra time or frequency resources in the communication system. Fig. 1 therefore discloses a RIS arrangement according to an example of the invention. The RIS arrangement 100 comprises an array of passive reflective elements 120 configured to reflect an incoming signal 710. The RIS arrangement further comprise a controller 110 configured to control the array of passive reflective elements 120 to change a reflection delay or a reflection direction for the incoming signal 710. The controller 110 is further configured to obtain one or more information bits, and to encode the one or more information bits into the incoming signal 710 by controlling a reflection delay or a reflection direction for the incoming signal 710 based on the one or more information bits. The novel encoding scheme may be referred to as RIS encoding.

The passive reflective elements of the array 120 may be considered as passive or nearly passive, and the reflective elements do not need any dedicated energy source for operation. The reflective elements may be viewed as a contiguous surface, and ideally any point can shape the wave impinging upon it e.g., by soft programming. The reflective elements are not affected by receiver noise, since ideally the reflective elements do not need any analogue to digital converters (ADCs), digital to analogue converter (DACs), or power amplification for operation. As a result, the reflective elements of the RIS arrangement do not amplify nor introduce noise when reflecting incoming signals and also provide an inherently full-duplex transmission. Further, the reflective elements have full-band response, since they can work at any operating frequency and they can be easily deployed, e.g., on the facades of buildings, ceilings of factories, indoor spaces, on human clothing, etc.

The RIS controller 110 may group m number of information bits and based on the choice of channel encoder and cyclic redundancy check (CRC) availability encode the m bits into n number of bits, where n is equal or larger than m. The controller 110 of the RIS arrangement 100 may be implemented in a processor having suitable capabilities. The RIS controller 110 is capable of configuring or programming the reflective elements of the array 120. Each reflective element may be connected to a tunable chip to change its load impedance, such as a PIN diode or varactor, and the RIS controller 110 may be implemented in a control circuit board connected to the reflective elements for controlling them so as to altering the reflection delay or the refection angle of the incoming signal 710 at the RIS arrangement 100. The RIS controller 110 may also be configured to communicate with a network access device 300 or any other network node of the communication system via a separate control channel so as to control the reflection delay or the reflection angle of the incoming signal 710, which in turn leads to controlling the signal 710' reflected at a client device 500. As shown in Fig. 1 , the RIS arrangement 100 can be a standalone device in a communication system. In such case, the RIS arrangement 100 may be communicably coupled to one or more other communication devices in the communication system by means of a communication interface 130. However, the RIS arrangement 100 may in other examples be fully or partially integrated with network nodes of the communication system. In one example, such a RIS arrangement 100 is fully or partially integrated with a network access node, such as a base station (BS).

The RIS arrangement 100 may act as a tunable device where the network status via the network access node may determine how the RIS arrangement 100 should be operated. The network status may refer to the channel conditions between the RIS arrangement 100 and the client device 500, such as coverage status, mobility, etc. Hence, in such an implementation the functionality of the RIS arrangement 100 can be switched off and on depending on the network status of the system. In case that RIS encoding causes performance degradation in the system, the RIS controller 110 can set the array of passive reflective elements 120 in a non-encoding mode (i.e. OFF mode) and if it is beneficial to use RIS encoding, the array of passive reflective elements 120 can be set in a RIS encoding mode (i.e. ON mode). In the latter mode the n bits are encoded into property variations in the metasurfaces of the RIS arrangement 100 by manipulating the reflection delay or the reflection angle of the incoming signal 710.

Fig. 2 shows a flow chart of a corresponding method 200 which may be executed in a RIS arrangement 100, such as the one shown in Fig. 1. Hence, RIS arrangement 100 comprises an array of passive reflective elements 120 and a controller 110 configured as previously described. The method 200 comprises obtaining 202 one or more information bits. The method 200 further comprises encoding 204 the one or more information bits into the incoming signal 710 by controlling a reflection delay or a reflection direction for the incoming signal 710 based on the one or more information bits.

Fig. 3 shows a network access node 300 according to an example of the invention. In the example shown in Fig. 3, the network access node 300 comprises a processor 302, a transceiver 304 and a memory 306. The processor 302 is coupled to the transceiver 304 and the memory 306 by communication means 308 known in the art. The network access node 300 may be configured for both wireless and wired communications in a communication system. The wireless communication capability may be provided with an antenna or antenna array 310 coupled to the transceiver 304, while the wired communication capability may be provided with a wired communication interface 312 e.g., coupled to the transceiver 304. That the network access node 300 is configured to perform certain actions can in this disclosure be understood to mean that the network access node 300 comprises suitable means, such as e.g., the processor 302 and the transceiver 304, configured to perform said actions.

According to examples of the invention and with reference to Fig. 3 and 7, the network access node 300 is configured to transmit a RIS control message 810 to a RIS arrangement 100. The RIS control message 810 indicates one or more encoding control parameters for controlling an array of passive reflective elements 120 for encoding one or more information bits.

Fig. 4 shows a flow chart of a corresponding method 400 which may be executed in a network access node 300, such as the one shown in Fig. 3. The method 400 comprises transmitting 402 a RIS control message 810 to a RIS arrangement 100. The RIS control message 810 indicates one or more encoding control parameters for controlling an array of passive reflective elements 120 for encoding one or more information bits.

Fig. 5 shows a client device 500 according to an example of the invention. In the example shown in Fig. 5, the client device 500 comprises a processor 502, a transceiver 504 and a memory 506. The processor 502 is coupled to the transceiver 504 and the memory 506 by communication means 508 known in the art. The client device 500 further comprises an antenna or antenna array 510 coupled to the transceiver 504, which means that the client device 500 is configured for wireless communications in a communication system. That the client device 500 is configured to perform certain actions can in this disclosure be understood to mean that the client device 500 comprises suitable means, such as e.g. the processor 502 and the transceiver 504, configured to perform said actions.

According to examples of the invention and with reference to Fig. 5 and 7, the client device 500 is configured to receive a signal 710' from a RIS arrangement 100. The signal 710' comprises one or more encoded information bits. The client device 500 is further configured decode the signal 710' to derive the one or more encoded information bits based on determining a RIS reflection delay or a RIS reflection direction of the signal 710'.

Fig. 6 shows a flow chart of a corresponding method 600 which may be executed in a client device 500, such as the one shown in Fig. 5. The method 600 comprises receiving 602 a signal 710' from a RIS arrangement 100. The signal 710' comprises one or more encoded information bits. The method 600 further comprises decoding 604 the signal 710' to derive the one or more encoded information bits based on determining a RIS reflection delay or a RIS reflection direction of the signal 710'. Fig. 7 shows a communication system 700 according to an example of the invention. The communication system 700 comprises a client device 500 and a network access node 300 configured to operate in the communication system 700. The communication system 700 further comprises a RIS arrangement 100 which is located, in a radio propagation point of view, between the network access node 300 and the client device 500. The network access node 300 may be a base station (BS), such as a gNB of a 3GPP radio access network (RAN) while the client device may be a so-called user equipment (UE). The network access node 300 is configured make downlink transmissions directly or indirectly via the RIS arrangement 100 to the client device 500.

It is illustrated in Fig. 7 how the network access node 300 makes a downlink transmission to the client device 500 in a communication signal 710 which is reflected at the RIS arrangement 100 such that the client device 500 receives a reflected communication signal 710'. In the reverse direction the client device 500 may be configured to make uplink transmissions to the network access node 300, which is however not shown in the Figs.

The RIS arrangement 100 may be communicably coupled to the gNB 300 by means of suitable communication interfaces 130, being wired and/or wireless. The communication system 700 may in a non-limiting example conform to 3GPP standards, such as 5G new radio (NR). Therefore, in the following disclosure further examples of the invention will be presented and described. For improved understanding, the mentioned examples are set in 3GPP communication context hence the expressions, terminology, architecture, protocols, etc. used. This further means that the client device 500 may be denoted a UE and the network access node 300 denoted a gNB. However, examples of the invention are not limited thereto.

Fig. 8 illustrates an example of the invention when information bits are encoded by controlling the reflection delay of the incoming signal 710 at the RIS arrangement 100. The example may also be considered as a time-of-arrival (ToA) based encoding via the RIS arrangement 100. In this example, the gNB 500 act as the transmitter sending its communication message to a UE 500 which act as the intended receiver of the communication message. The RIS arrangement 100, including an array of passive metasurface elements 120 and a controller 110, is therefore configured to control the ToA of the incoming waveform reflecting from the RIS arrangement 100. In the RIS arrangement 100, the RIS controller 110 can control the physical properties of the metasurfaces by thinning and thickening the elements in the array 120 in different configurations thereby controlling the reflection delay of the incoming signal 710. This also implies that the UE 500 will be configured to decode the incoming signal 710' at the UE 500 to derive the one or more encoded information bits based on determining the duration of the RIS reflection delay.

By manipulating the physical properties of the array of elements as explained, the RIS controller 110 may control the arrival of an orthogonal frequency-division multiplexing (OFDM) symbol reflected from the RIS arrangement 100. An extra delay element _dn will be introduced to the end-to-end channel, i.e., from the gNB 300 to the RIS arrangement 100 to the UE 500, in addition to existing delays of a propagation path from the gNB 300 to the nth element of the RIS arrangement 100 and thereafter to the UE 500, such that the propagation channel can be expressed as: where N is the number of metasurface reflective elements in the RIS arrangement 100, L _a is the number of paths from the gNB 300 to the RIS arrangement 100, L _b is the number of paths from the RIS arrangement 100 to the UE 500, a _n ^l is the propagation path loss of the Zth path from the gNB 300 to the nth reflective element, ' ^s the propagation path loss of the pth path from the gNB 300 to the nth reflective element, y is the operating signal-to-noise ratio, 6 _n is radiating a fraction of the nth reflective element such that 6 _n < 1, f _c the carrier frequency of the modulated signal, is the delay from the Zth path from the gNB 300 to the nth reflective element, is the delay from the pth path from the gNB 300 to the nth reflective element, and t _n is the reflective delay introduced by the RIS arrangement 100.

The ToA is therefore adjusted in the time domain of a so-called synthesized path from the RIS arrangement 100 to the UE 500. The synthesized path may be considered as the radio path altered or manipulated by the RIS arrangement 100 for the present encoding/decoding scheme. The units of the synthesized path to be controlled can be specified, but a simple way is using integer samples noting that each OFDM symbol comprises Nfft number of samples in a 3GPP 5G system.

In Fig. 8, an example is given when the reflection delay is implemented over 14 OFDM symbols in a transmission time interval (TTI). A cyclic prefix (CP) boundary line is also show which is the time instant where the CP may be effectively removed. This may be done by generating a pulse on the trailing edge of the estimated CP boundary of each OFDM symbol. Different techniques are available for removing and estimating where the CP ends, e.g., FFT window timing estimator or sign bit autocorrelator. The dashed arrow illustrates how the reflection delay can be adjusted in the left or right direction for encoding information bits in the CP. The reflection delay may be adjusted in step sizes of milliseconds or any other time unit by controlling the propagation reflection delay of the synthesized path. For example, a reflection delay in the synthesized propagation path by 1/2 samples can indicate that a bit “1” has been transmitted. As long as the adjusted reflection delay is less than the CP duration of the frame, no inter-symbol-interference (ISI) will occur and will therefore not negatively affect the performance of the communication system 700. Hence, if the incoming signal 710 at the RIS arrangement 100 carries a set of OFDM symbols encoding the information bits comprises controlling the duration of the reflection delay in a CP of a OFDM symbol in the set of OFDM symbols. Different implementation cases of such encoding are herein presented.

In an example of the invention, encoding the information bits comprises controlling the duration of the reflection delay in the cyclic prefix of the OFDM symbol in relation to a duration of a reflection delay in a cyclic prefix of a previous OFDM symbol in the set of OFDM symbols. In other words, by comparing a reflection delay difference of the current OFDM symbol to the previous OFDM symbol in the set of OFDM symbols. For example,

IF t(n+ 1 )-t(n) < 0 transmitted bit ’0’ is indicated,

IF t(n+1)-t(n) >= 0 transmitted bit T is indicated, where t(n) refers to the previous OFDM symbol’s time of arrival, and t(n+1) is the current OFDM symbol’s ToA. Hence, the UE 500 will correspondingly be configured to decode the encoded information bits accordingly.

In another example, encoding the information bits comprises controlling the duration of the reflection delay in the cyclic prefix of the OFDM symbol in relation to a duration of a reflection delay in a cyclic prefix of a first OFDM symbol in the set of OFDM symbols. In other words, comparing a reflection delay difference of the current OFDM symbol to the first OFDM symbol in the set of OFDM symbols. The first OFDM symbol may e.g., be the first OFDM symbol of a frame. For example,

IF t(n+ 1 )-t(0) < 0 transmitted bit ’0’ is indicated,

IF t(n+1)-t(0) >= 0 transmitted bit ’1 is indicated, where t(0) refers the first OFDM symbol’s time of arrival, and t(n+1) is the current OFDM symbol’s ToA. Hence, the UE 500 will correspondingly be configured to decode the encoded information bits accordingly.

In yet further example of the invention, encoding the information bits comprises controlling the duration of the reflection delay in the cyclic prefix of the OFDM symbol in relation to a threshold value. Hence, in this example a threshold value A is introduced for encoding the information bits. It is useful for defining different interval between time of arrival of OFDM signal in the UE

500. Two main cases may be identified in this respect.

In a first case, by using a reflection delay difference compared to the threshold value A. For example, encoding 2 bits may be implemented such that:

IF t(n+1)-t(n) < A transmitted bits ’00’ are indicated,

ELSE IF t(n+1)-t(n) < 0 transmitted bits ’0T are indicated,

ELSE IF t(n+1)-t(n) < A transmitted bits ’10’ are indicated, ELSE transmitted bits ’1 T are indicated.

Hence, the UE 500 will correspondingly be configured to decode the encoded information bits accordingly.

In a second case, by using an absolute reflection delay difference compared to the threshold value A encoding 2 bits may be implemented such that:

IF |t(n+1)-t(n)| < A indicates bits ’00’,

ELSE IF |t(n+1)-t(n)| < 2A transmitted bits ’0T are indicated,

ELSE IF |t(n+1)-t(n)| < 3A transmitted bits ’10’ are indicated,

ELSE IF |t(n+1)-t(n)| < 4A transmitted bits ’11 ' are indicated.

Hence, the UE 500 will be configured to decode the encoded information bits accordingly.

The case of using absolute delay difference gives more freedom of adjusting reflection delay in case a bit sequence is biased towards one direction, i.e. , a bit sequence comprising of all 1s or all 0s.

From the above examples it is noted that the threshold value A has to be selected carefully. The threshold value or values A may be preconfigured and given by a communication standard. The threshold value A may depend on the propagation properties of the radio channel between the transmitter (gNB) and the receiver (UE). In addition to the propagation properties, the value of the threshold may also be dependent on the number of bits to be encoded.

Fig. 9 instead illustrates an example of the invention when the information bits are encoded by controlling the reflection angle of the incoming signal 710 at the RIS arrangement 100. In other words, encoding the one or more information bits comprises controlling an azimuth reflection angle and/or an elevation reflection angle of the reflection direction of the incoming signal 710 at the RIS arrangement 100. This also implies that the UE 500 will be configured to decode the signal 710' at the UE 500 to derive the one or more encoded information bits based on determining the azimuth reflection angle and/or the elevation reflection angle. The example shown in Fig. 9 may hence be considered as an angle-of-departure (AoD) based encoding via the RIS arrangement 100. By using of a large number of reflection elements in the RIS arrangement 100, the incoming signal 710 can be reflected in a highly directional beam towards to the target user i.e., the UE 500. Depending on the RIS technology, the RIS arrangement 100 can change the direction of reflection or refract the signal, similar to a lens in optics. In similar ways with ToA based encoding as described with reference to Fig. 8, the AoD of the reflected path from the RIS arrangement 100 to the UE 500 can be adjusted/controlled, and such an adjustment can be detected by the UE 500 to decode the information bits encoded into the signal 710'. This is especially the case under a perfect line- of-sight (LoS) scenario between the RIS arrangement 100 and the UE 500.

In examples of the invention, encoding the one or more information bits comprises controlling the azimuth reflection angle or the elevation reflection angle. This means encoding information bits in one dimension only. Hence, each shift in an angular dimension can imply an encoding state such as for encoding of bits using reflective delay which is also encoding in one dimension.

In further examples of the invention, encoding the one or more information bits comprises controlling the azimuth reflection angle and the elevation reflection angle based on a two- dimensional codebook grid given by the azimuth reflection angle and the elevation reflection angle. Fig. 9 shows this particular example where a two-dimensional (2D) AoD codebook structure is illustrated, and in each time instance, the synthesized reflecting path from the RIS arrangement 100 can select one AoD from the 2D codebook, which contains both azimuth and elevation angles. Assuming that the current AoD uses the angles corresponding to the grid marked in Fig. 9, in the RIS based AoD encoding, the AoD can move in 8 different directions or stay put, which yields in total more than 3 bits that can be encoded by adjusting the azimuth reflection angle and the elevation reflection angle. In a non-limiting example, the reflection angle encoding can be implemented as follows:

• IF at most only azimuth or elevation reflection angle is changed, i.e., the grid remains the same or moves left, right, up, and down (i.e. the 4 solid arrows), bit ‘0’ is indicated;

• ELSE if both azimuth and elevation reflection angles are changed, i.e., the grid moves up-left, up-right, down-left, down-right (i.e. the 4 dashed arrows), bit ‘T is indicated.

When encoding two bits, bit encoding may be implemented as the following where the elevation angle axis label is North (Up) and Azimuth angle axis label is West (Left):

• North-West or North-East indicates transmitted bits ‘00’, South-West or South-East indicates transmitted bits ‘0T,

North or South indicates transmitted bits ‘10’,

West or East indicates transmitted bits ‘11’.

At the UE 500 side decoding information bits encoded with the 2D codebook. The UE 500 can run an estimation procedure for determining the transmitted 2D codebook. The UE 500 can search the AoDs exhaustively of the incoming signal 710' and use the angles/directions with the largest gain for deriving the relevant angle information for decoding. In another example, the UE 500 may deploy adaptive algorithm considering channel information for iteratively reducing the set of candidates so as to decode the incoming signal 710'.

Moreover, Fig. 10 shows a signaling diagram illustrating the interaction between a gNB 300, a RIS arrangement 100 and a UE 500 in a 5G communication system. Both aperiodic and semi- persistent encoding is discussed. Aperiodic encoding refers to one time encoding via the RIS arrangement 100. Semi-persistent encoding on the other hands means that RIS encoding stays active, once an activation message received until receiving a deactivation message. In the disclosed example, control information bits or data information bits are encoded in a CP thereby leveraging RIS capabilities to modify channel characteristics in terms of reflection delay or reflection angle. In this respect information about the decoding capability/incapability of the UE 500 may be required. It is also beneficial to be able to activate/deactivate or periodically trigger the RIS encoding mechanism so that the network via the gNB 300 can use the mechanism of RIS encoding when the channel conditions and/or UE location are suitable for improved performance. However, the RIS arrangement 100 may also be used for other purposes, such as coverage enhancement, interference coordination, assisting beamforming, etc. So, it may be up to the network to identify the opportune time periods when RIS encoding should be activated or not.

For the case when the one or more information bits are associated with control information, such control information may e.g., relate to any of: system information such as scheduling information for downlink data transmission, ACK/NACK feedback of a hybrid automatic repeat request (HARQ) procedure for uplink transmissions, phase configuration, scheduling request (SR) and conveying scheduling information, synchronization signal (SS), physical broadcast channel (PBCH) blocks, and physical random access channel (PRACH). The control information may be used by the UE 500 to select proper transmission and/or reception parameters, for UE positioning, etc. First, the signaling and interaction between the gNB 300 and the UE 500 is described with reference to Fig. 10. Thereafter, the signaling and interaction between the gNB 300 and the RIS arrangement 100 also with reference to Fig. 10 is described.

Step 1 in Fig. 10: the gNB 300 transmits a capability enquiry message 850 to the UE 500. The capability enquiry message 850 indicates a request for information about the RIS decoding capability of the UE 500. The capability enquiry message 850 hence enables to initiate UE capability transfer applicable for a UE in the RRC connected state. The gNB 300 may initiate the UE capability transfer if it requires additional UE capability information e.g., as defined in 3GPP TS 38.331 , 5.6.1.

Step 2 in Fig. 10: the UE 500 responds to the capability enquiry message 850 by transmitting a capability message 840 to the gNB 300. The capability message 840 indicates a RIS decoding capability of the UE 500, e.g., RIS CP decoding capability/incapability and other relevant decoding capabilities such as number of encoded bits, number of bits per encoded symbol, symbol length, etc. The content of the capability message 840 will be dependent on the content of the capability enquiry message 850. Hence, additional capability information related to RIS decoding capability may be included in the capability message 840.

Step 3 in Fig. 10: the gNB 300 based on the received capability message 840 from the UE 500 transmits a configuration message 820 to the UE 500. The configuration message 820 indicates a RIS decoding configuration for the UE 500. The configuration message 820 may e.g., be a radio resource control (RRC) reconfiguration message and include the needed configuration information elements (lEs) and decoding parameters to be used by the UE 500 for RIS CP decoding, including e.g., the format of the encoded information. The configuration message 820 may further indicate aperiodic decoding or semi-persistent decoding.

Step 4 in Fig. 10: the UE 500 transmits a RRC reconfiguration complete message 860 to the gNB 300 and hence acknowledge the configuration in the configuration message 820 from the gNB 300. This means that the gNB 300 knows that the UE 500 is ready for RIS encoding/decoding.

Step 5 in Fig. 10: the gNB 300 schedules one or more physical downlink shared channels (PDSCHs) for downlink transmission to the UE 500 by the transmission of downlink control information (DCI) indicating the downlink transmission. Step 6 in Fig. 10: the gNB 300 transmit an activation message 830 to the UE 500. The activation message 830 indicates the activation of the RIS decoding configuration that was indicated in the configuration message 820. The activation message 830 may be in the form of a medium access control (MAC) control element (CE) or any other suitable signaling. After reception of the activation message 830, the UE 500 assumes that RIS CP encoding is active and prepares to decode information encoded in a CP of a PDSCH based on the configuration message 820.

Step 7 in Fig. 10: the gNB 300 transmits one or more PDSCHs comprising encoded CPs to the UE 500 via the RIS arrangement 100. The incoming signal 710 carrying the one or more PDSCHs at the RIS arrangement 100 is encoded by controlling the reflection delay or the reflection angle of the incoming signal 710. The signal reflected by the RIS arrangement 100, i.e., signal 710', will propagate from the RIS arrangement 100 to the UE 500.

Step 8 in Fig. 10: the UE 500 transmits uplink control information (UCI) including separate or common ACK/NACK according to a HARQ procedure for providing feedback about the decoding outcome of the RIS decoding at the UE 500. A HARQ-ACK resulting from the CP decoding may be separately encoded or jointly encoded with a HARQ-ACK resulting from decoding of payload data of the received symbol.

Step 9 in Fig. 10: the gNB 300 transmits a deactivation message 830 to the UE 500 for deactivating RIS encoding when the transmission of the one or more PDSCHs in the downlink transmission have ended. The deactivation message 830 may also be in the form of a MAC CE e.g., in case of semi-persistent RIS encoding/decoding mode.

After reception of the deactivation message 830, the UE 500 assumes that no information is expected to be RIS encoded/decoded until receiving a new activation message 830 from the gNB 300.

Steps 10 to 13 in Fig. 10 describes the interaction between the gNB 300 and the RIS arrangement 100 and may be considered as a control and adaptation loop for RIS encoding. Mentioned steps 10 to 13 of the control and adaptation loop may be performed in parallel to steps 1 to 9, and especially in parallel to the step when the gNB 300 transmits encoded information to the UE 500 in a PDSCH via the RIS arrangement 100. However, steps 10 to 13 may also be performed offline which means that the mentioned steps 10 to 13 can be performed independently from the other steps and during another time period. Step 10 in Fig. 10: the gNB 300 triggers measurement collection at the RIS arrangement 100 by transmitting an initiate measurement message 870 to the RIS arrangement 100. The initiate measurement message 870 indicates that the RIS arrangement 100 should start taking measurements and send measurement reports (MPs) to the gNB 300. Furthermore, the initiate measurement message 870 may also indicate the type of measurements, periodicity of measurements, report format, radio resources to be used for reporting, reporting procedure, etc.

The RIS arrangement 100 may measure downlink (DL) reference signals (RS) transmitted by the gNB 300 and/or uplink (UL) RS transmitted by the UE 500. These measurements may be needed in order to derive information about the channel conditions between the RIS arrangement 100 and the gNB 300, on one hand, and the channel conditions between the UE 500 and the RIS arrangement 100 on the other hand.

Step 11 in Fig. 10: the gNB 300 directly or indirectly controls the RIS elements of the RIS arrangement 100 thereby also directly or indirectly controlling the reflection delay or the reflection angle of the incoming signal 710 at the RIS arrangement 100. In this respect the gNB 300 may transmit a RIS control message 810 to a RIS arrangement 100. The RIS control message 810 indicates one or more encoding control parameters for controlling the array of passive reflective elements 120 for encoding one or more information bits.

The controller 110 of the RIS arrangement 100 controls the array of passive reflective elements 120 for encoding the one or more information bits based on the RIS control message 810 received from the gNB 300.

Step 12 in Fig. 10: the RIS arrangement 100 triggered by the gNB 300 transmits measurement reports MPs to the gNB 300. The measurement reports may have the reporting format and be transmitted in radio resources indicated in the initiate measurement message 870.

The gNB 300 continuously updates the encoding control parameters based on the measurement reports MRs received from the RIS arrangement 100. The updated encoding control parameters may indicate how the reflection delay or the reflection angel should be adapted to the changing channel conditions derived from the measurement reports MPs for optimal encoding. A data log may be collected at the gNB and the data log may comprise the measurement reports. Based on such a data log the gNB 300 may fine tune the encoding control parameters e.g., by using a maximum likelihood (ML) algorithm. The gNB 300 therefore transmits one or more updated RIS control messages 810 indicating the updated encoding control parameters to the RIS arrangement 100. The controller 110 at the RIS arrangement controls the array of passive reflective elements 120 based on the updated RIS control messages 810 which indicates the updated encoding control parameters.

As previously disclosed, the RIS arrangement 100 may in examples be integrated with or at least controlled by the gNB 300. This also implies that the network access node 300 may provide the information bits to be encoded at the RIS arrangement 100, e.g., by transmitting an indication of the information bits over a suitable communication interface to the RIS arrangement 100.

The network access node herein may also be denoted as a radio network access node, an access network access node, an access point, or a base station, e.g. a Radio Base Station (RBS), which in some networks may be referred to as transmitter, “gNB”, “gNodeB”, “eNB”, “eNodeB”, “NodeB” or “B node”, depending on the technology and terminology used. The radio network access nodes may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The radio network access node can be a Station (STA), which is any device that contains an IEEE 802.11 -conformant Media Access Control and Physical Layer interface to the Wireless Medium. The radio network access node may also be a base station (BS) corresponding to the fifth generation (5G) wireless systems.

The client device herein, may be denoted as a user device, a User Equipment (UE), a mobile station, an internet of things (loT) device, a sensor device, a wireless terminal and/or a mobile terminal, is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UEs may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability. The UEs in this context may be, for example, portable, pocket-storable, hand-held, computer- comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via a radio access network (RAN), with another communication entity, such as another receiver or a server. The UE can be a Station (STA), which is any device that contains an IEEE 802.11- conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM). The UE may also be configured for communication in 3GPP related LTE and LTE-Advanced, in WiMAX and its evolution, and in fifth generation (5G) wireless systems, such as New Radio (NR).

Furthermore, any method according to examples of the invention may be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium may comprise essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), an EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive.

Moreover, it should be realized that the client device and the network access node comprises the necessary communication capabilities in the form of e.g., functions, means, units, elements, etc., for performing examples of the invention. Examples of other such means, units, elements and functions are: processors, memory, buffers, control logic, encoders, decoders, rate matchers, de-rate matchers, mapping units, multipliers, decision units, selecting units, switches, interleavers, de-interleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, MSDs, TCM encoder, TCM decoder, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together for performing the solution.

Therefore, the processor(s) of the client device and the network access node may comprise, e.g., one or more instances of a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The expression “processor” may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like.

Finally, it should be understood that the invention is not limited to the examples described above, but also relates to and incorporates all examples within the scope of the appended independent claims.