ETSI GR RIS 004 V1.1.1 (2025-03)

Reconfigurable Intelligent Surfaces (RIS); Implementation and Practical Considerations

DGR/RIS-004

General Information

• Status: Not Published
• Technical Committee: RIS - Reconfigurable Intelligent Surfaces
• Current Stage: 12 - Citation in the OJ (auto-insert)
• Due Date: 19-Feb-2025
• Completion Date: 19-Mar-2025

Standards Content (Sample)

GROUP REPORT
Reconfigurable Intelligent Surfaces (RIS);
Implementation and Practical Considerations
Disclaimer
The present document has been produced and approved by the Reconfigurable Intelligent Surfaces (RIS) ETSI Industry
Specification Group (ISG) and represents the views of those members who participated in this ISG.
It does not necessarily represent the views of the entire ETSI membership.

2 ETSI GR RIS 004 V1.1.1 (2025-03)

Reference
DGR/RIS-004
Keywords
cellular, radio, radio measurements, RIS

ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis Cedex - FRANCE

Tel.: [phone]  Fax: [phone]

Siret N° 348 623 562 00017 - APE 7112B
Association à but non lucratif enregistrée à la
Sous-Préfecture de Grasse (06) N° w061004871

Important notice
The present document can be downloaded from the
ETSI Search & Browse Standards application.
The present document may be made available in electronic versions and/or in print. The content of any electronic and/or
print versions of the present document shall not be modified without the prior written authorization of ETSI. In case of any
existing or perceived difference in contents between such versions and/or in print, the prevailing version of an ETSI
deliverable is the one made publicly available in PDF format on ETSI deliver repository.
Users should be aware that the present document may be revised or have its status changed,
this information is available in the Milestones listing.
If you find errors in the present document, please send your comments to
the relevant service listed under Committee Support Staff.
If you find a security vulnerability in the present document, please report it through our
Coordinated Vulnerability Disclosure (CVD) program.
Notice of disclaimer & limitation of liability
The information provided in the present deliverable is directed solely to professionals who have the appropriate degree of
experience to understand and interpret its content in accordance with generally accepted engineering or
other professional standard and applicable regulations.
No recommendation as to products and services or vendors is made or should be implied.
No representation or warranty is made that this deliverable is technically accurate or sufficient or conforms to any law
and/or governmental rule and/or regulation and further, no representation or warranty is made of merchantability or fitness
for any particular purpose or against infringement of intellectual property rights.
In no event shall ETSI be held liable for loss of profits or any other incidental or consequential damages.

Any software contained in this deliverable is provided "AS IS" with no warranties, express or implied, including but not
limited to, the warranties of merchantability, fitness for a particular purpose and non-infringement of intellectual property
rights and ETSI shall not be held liable in any event for any damages whatsoever (including, without limitation, damages
for loss of profits, business interruption, loss of information, or any other pecuniary loss) arising out of or related to the use
of or inability to use the software.
Copyright Notification
No part may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm except as authorized by written permission of ETSI.
The content of the PDF version shall not be modified without the written authorization of ETSI.
The copyright and the foregoing restriction extend to reproduction in all media.

© ETSI 2025.
All rights reserved.
ETSI
3 ETSI GR RIS 004 V1.1.1 (2025-03)
Contents
Intellectual Property Rights . 4
Foreword . 4
Modal verbs terminology . 4
1 Scope . 5
2 References . 5
2.1 Normative references . 5
2.2 Informative references . 5
3 Definition of terms, symbols and abbreviations . 6
3.1 Terms . 6
3.2 Symbols . 6
3.3 Abbreviations . 6
4 General hardware aspects of RIS . 7
4.0 Unit-cell principle of operation . 7
4.1 Quantized Phase Shifts . 7
4.2 Metasurface designs . 9
4.3 Switching element . 9
4.4 RIS controller . 14
4.5 RIS interfaces . 14
4.6 RIS power source . 15
4.7 Design of RIS control circuit . 17
4.7.0 Introduction. 17
4.7.1 General . 17
4.7.2 RIS serial communication control . 18
4.7.3 RIS serial parallel communication control . 18
4.7.4 RIS multiple-tile control . 19
4.7.5 RIS multiple-tile hierarchical control . 21
4.7.6 RIS transistor-based matrix control . 22
5 Design requirements and practical implications for RIS types . 23
5.1 General considerations including EE, EMF and coexistence . 23
5.1.1 Regulatory requirements . 23
5.1.2 RIS bandwidth of influence . 23
5.1.3 Side Lobe Level (SLL) reduction techniques . 24
5.2 Reflective RIS . 28
5.3 Refractive/Transmissive RIS . 30
5.4 Absorptive RIS . 31
5.5 STAR-RIS . 33
5.6 Multi-functional RIS . 35
6 RIS prototypes, trials and measurements . 37
6.1 Evaluation of spectral contrast in RIS prototypes . 37
6.2 Trial results in typical deployment scenarios . 37
6.3 RIS Bistatic RCS Measurements . 46
6.4 RIS Radiation Pattern Measurement . 51
7 Cost, complexity and energy-efficiency analysis of RIS . 54
7.1 RIS device cost and complexity . 54
7.2 RIS deployment costs . 55
7.3 Comparative analysis . 56
7.4 Other practical considerations . 57
8 Conclusion and Recommendations . 58
History . 59

ETSI
4 ETSI GR RIS 004 V1.1.1 (2025-03)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The declarations
pertaining to these essential IPRs, if any, are publicly available for ETSI members and non-members, and can be
found in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to
ETSI in respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the
ETSI IPR online database.
Pursuant to the ETSI Directives including the ETSI IPR Policy, no investigation regarding the essentiality of IPRs,
including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not
referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become,
essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
DECT™, PLUGTESTS™, UMTS™ and the ETSI logo are trademarks of ETSI registered for the benefit of its
Members. 3GPP™, LTE™ and 5G™ logo are trademarks of ETSI registered for the benefit of its Members and of the
3GPP Organizational Partners. oneM2M™ logo is a trademark of ETSI registered for the benefit of its Members and of ®
the oneM2M Partners. GSM and the GSM logo are trademarks registered and owned by the GSM Association.
Foreword
This Group Report (GR) has been produced by ETSI Industry Specification Group (ISG) Reconfigurable Intelligent
Surfaces (RIS).
Modal verbs terminology
In the present document "should", "should not", "may", "need not", "will", "will not", "can" and "cannot" are to be
interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.

ETSI
5 ETSI GR RIS 004 V1.1.1 (2025-03)
1 Scope
The present document identifies Reconfigurable Intelligent Surfaces (RIS) relevant use cases with corresponding
general Key-Performance-Indicators (KPIs), deployment scenarios operational requirements for each identified use
case. KPIs and operational requirements will include system/link performance, spectrum, co-existence and security.
2 References
2.1 Normative references
Normative references are not applicable in the present document.
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI GR RIS 001: "Reconfigurable Intelligent Surfaces (RIS); Use Cases, Deployment Scenarios
and Requirements".
[i.2] ETSI GR RIS 002: "Reconfigurable Intelligent Surfaces (RIS); Technological challenges,
architecture and impact on standardization".
[i.3] ETSI GR RIS 003: "Reconfigurable Intelligent Surfaces (RIS); Communication Models, Channel
Models, Channel Estimation and Evaluation Methodology".
[i.4] George C. Alexandropoulos, et. all: "RIS-Enabled Smart Wireless Environments: Deployment
Scenarios, Network Architecture, Bandwidth and Area of Influence", submitted to EURASIP
Journal.
[i.5] Directive 2014/53/EU of the European Parliament and of the Council of 16 April 2014.
[i.6] A. Haskou, and H. Khaleghi: "On the effect of RIS phase quantization on communications system
performances", 2023 International Wireless Communications and Mobile Computing (IWCMC),
Marrakesh, Morocco, pp. 1406-1411, 2023.
[i.7] ETSI TS 138 101-1: "5G; NR; User Equipment (UE) radio transmission and reception; Part 1:
Range 1 Standalone (3GPP TS 38.101-1 Release 17)".
[i.8] A. Tishchenko, A. Ali, A. Araghi, P. Botham, F. Burton and M. Khalily: "Autonomous
th
Reconfigurable Intelligent Surface based on Highly-Efficient Solar Cells," 2023 17 European
Conference on Antennas and Propagation (EuCAP), Florence, Italy, pp. 1-5, 2023.
[i.9] A. Haskou and H. Khaleghi: "An Efficient and Easy-to-Implement Method for SLL Reduction in
RIS-Aided Systems". TechRxiv, 31-August-2023.
[i.10] H. Taghvaee et al.: "Scalability Analysis of Programmable Metasurfaces for Beam Steering", in
IEEE Access, vol. 8, pp. 105320-105334, 2020.
[i.11] Fangzhou Wang, and A. Lee Swindlehurst: "Applications of Absorptive Reconfigurable Intelligent
Surfaces in Interference Mitigation and Physical Layer Security", 2023.
ETSI
6 ETSI GR RIS 004 V1.1.1 (2025-03)
[i.12] S. Zeng et al.: "Intelligent Omni-Surfaces: Reflection-Refraction Circuit Model, Full-Dimensional
Beamforming, and System Implementation", in IEEE Transactions on Communications, vol. 70,
no. 11, pp. 7711-7727, November. 2022.
[i.13] Recommendation ITU-R SM.329: "Unwanted emissions in the spurious domain".
[i.14] ETSI GR RIS 006: "Reconfigurable Intelligent Surfaces (RIS); Multi-functional Reconfigurable
Intelligent Surfaces (RIS): Modelling, Optimisation, and Operation".
[i.15] R. Liu, J. Dou, P. Li, J. Wu and Y. Cui: "Simulation and Field Trial Results of Reconfigurable
Intelligent Surfaces in 5G Networks", in IEEE Access, vol. 10, pp. 122786-122795, 2022.
[i.16] M. Rossanese, P. Mursia, A. Garcia-Saavedra, V. Sciancalepore, A. Asadi, and X. Costa-Perez:
"Design and validation of scalable reconfigurable intelligent surfaces", Computer Networks,
vol. 241, no.110208, 2024.
[i.17] H. Rajabalipanah, K. Rouhi, A. Abdolali, S. Iqbal, L. Zhang and S. Liu: "Real-time terahertz
meta-cryptography using polarization-multiplexed graphene-based computer-generated
holograms", in Nanophotonics, vol. 9, no. 9, pp. 2861-2877, 2020.
[i.18] J. B. Gros, V. Popov, M. A. Odit, V. Lenets, G. Lerosey: "A Reconfigurable Intelligent Surface at
mmWave Based on a Binary Phase Tunable Metasurface", IEEE Open Journal of the
Communications Society, vol. 2, pp. 1055–1064, May 2021.
[i.19] ETSI GR RIS 007: "Reconfigurable Intelligent Surfaces (RIS); Near-field Channel Modeling and
Mechanics".
[i.20] C.-L. Liao, Y.-H. Lin, I. Lin, and C.-F. Yang: "Performance Evaluation of RU and RIS Based on
OTA Mode Near Field and Bistatic Measurement Systems", Antenna Measurement Techniques
Association Symposium (AMTA), October 2023.
[i.21] T.-H. Lee and W. D. Burnside: "Compact Range Reflector Edge Treatment Impact on Antenna
and Scattering Measurements", IEEE Trans. Antennas Propagat., vol. 45, no. 1, pp. 57-65,
January 1997.
[i.22] Kitayama D, Hama Y, Goto K, Miyachi K, Motegi T, Kagaya O.: "Transparent dynamic
metasurface for a visually unaffected reconfigurable intelligent surface: controlling
transmission/reflection and making a window into an RF lens", in Opt. Express, 29(18):29292-
29307, 2021.
3 Definition of terms, symbols and abbreviations
3.1 Terms
For the purposes of the present document, the following terms given in ETSI GR RIS 001 [i.1], in ETSI GR RIS 002
[i.2] and ETSI GR RIS 003 [i.3] apply.
3.2 Symbols
Void.
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
FPGA Field Programmable Gate Array
KPI Key Performance Index
RIS Reconfigurable Intelligent Surfaces
ETSI
7 ETSI GR RIS 004 V1.1.1 (2025-03)
4 General hardware aspects of RIS
4.0 Unit-cell principle of operation
The number of states of a unit-cell may be represented by a number of bits used based on the RIS implementation. RIS,
when built using locally switchable elements, can be described as a bit or state matrix and digitally controlled through
reconfigurable devices such as Field-Programmable Gate Arrays (FPGAs). Consequently, discretizing the
electromagnetic characteristics of the unit-cell (amplitude and phase) realizes simple wave manipulation with
straightforward tunability.
4.1 Quantized Phase Shifts
An ideal RIS unit cell is supposed to provide continuous phase shift values with infinite resolutions. However, in real-
world implementations, the resolutions of phase shifters/diodes/varactors are generally limited, resulting in quantized
phase shifts and degraded beamforming performances. The degradation of beamforming gains with different phase
quantization, imperfection, and RIS implementation constraints need to be thoroughly investigated. Figure 4.1.1-1 and
Figure 4.1.1-2 show the beamforming gain of RIS when a RIS aims to re-radiate the incident signals into different
steering directions for different number of RIS elements respectively. With 1-bit quantization, the beamforming gain is
generally about 3-4 dB less than the scenario with ideal phase shift control, which does not change significantly with
the number of elements on the RIS panel. The beamforming gain loss caused by phase quantization can only be
minimized in some certain re-radiating directions (e.g. when the re-radiation is subject to Snell's law), and such
re-radiating directions correspond to peaks in Figure 4.1.1-1 and Figure 4.1.1-2.
-0.5
-1
-1.5
1-bit
2-bit
Ideal
-2
-2.5
-3
-3.5
-4
-80 -60 -40 -20 0 20 40 60 80
Steering angle
Figure 4.1.1-1: 10 × 10 RIS beamforming gain for varying steering angle obtained
by using different phase shift control resolutions
ETSI
Beamforming gain loss (dB)
8 ETSI GR RIS 004 V1.1.1 (2025-03)
-0.5
-1
-1.5
1-bit
2-bit
Ideal
-2
-2.5
-3
-3.5
-4
-80 -60 -40 -20 0 20406080
Steering angle
NOTE: The incident angle is assumed to be -45 degrees in both examples. The yellow curve represents phase shift
control with infinite resolution. Blue and red curves represent phase shift controls with 1-bit and 2-bit
quantization, respectively.
Figure 4.1.1-2: 100 × 100 RIS beamforming gain for varying steering angle obtained
by using different phase shift control resolutions
An RIS unit cell can also provide phase shift values quantized with multiple bits. The function can be realized by using
phase shifters with higher resolution or multiple diodes in the same RIS unit. Figure 4.1.1-1 and Figure 4.1.1-2 show the
beamforming gain of RIS with 2-bit quantization, and the beamforming gain loss is generally less than 1 dB. Therefore,
the resolution of 2-bit quantization might be sufficient for RIS fabrication.
In some scenarios, the total number of control bits can be a constraint of RIS fabrication, which implies that the RIS can
be larger with low phase resolution per unit. Although the gain improvement of 2-bit quantization over 1-bit
quantization is around 3 dB, using 1-bit quantization leads to double RIS elements, which can provide around 6 dB
gain. Therefore, with constraints on the total control bits, multi-bit quantization may not be an optimal solution for RIS
fabrication. Generally, the requirement in terms of phase quantization can be determined depending on use-cases,
deployment scenarios, accuracy requirements, etc. Therefore, in certain cases, a finer phase quantization, while in other
cases coarser phase quantization may be needed.
Assuming an RIS with a large number of elements �, using far-field approximations, it can be shown that in absence of
� �
a direct Tx-Rx path, using i-bit phase quantization leads to a uniform phase quantization error ѱ ~��− , �.
�,� � �
� �
Then, the relative received signal level, i.e. the ratio between the received signal with phase quantization and the
received signal without phase quantization, is given by [i.9]:
� �� �
ѱ �� �
�,� �
� = = ���� � �
��������
�
� �
��
where � is the received signal using phase quantization, � is the received signal without phase quantization and
�� ��
�
ѱ is the difference between the optimal phase and the quantized phase.
�,�
Figure 4.1.1-3 shows the effect of the phase quantization on the relative received power (calculated as
� =20 ���(� )). As it can be seen, using 1-bit and 2-bit quantization lead to around 3,9 dB and 0,9 dB loss
�������� ��������
in the received power.
ETSI
Beamforming gain loss (dB)
9 ETSI GR RIS 004 V1.1.1 (2025-03)
-1
-2
-3
-4
02468 10
i-bit RIS
Figure 4.1.1-3: Effect of the quantization step on relative received power
In the case there is also a direct Tx-Rx path, the relative received signal is given by:
�
� � �� �
� √
� ����� �
�
� ��� �
�� �
� ��
� =
��������
�
� � ��
� √
�
� ��� �
��
� ��
where � is the free-space wavelength; � , � are respectively the distance from the RIS central element to Tx and Rx;
�� ��
� represents the overall gain between Tx and Rx through RIS; � is the direct distance between Tx and Rx and � is
� �
the overall direct path gain.
As it can be seen, in this case, the relative received signal is highly dependant on the direct path gain and distance, and
it is always higher than the case without direct path. Indeed, in the case where the direct path is the dominant one, i.e.
�
� �√��
�
≫ , this equation reduces to � ≈1. And in the case where the indirect path is the dominant one, i.e.
��������
� ��� �
� �� ��
�
�√�� � �
�
≫ , this equation reduces to � ≈ ���� � �. This means that, for example, in the case of a 1-bit RIS
�������� �
��� � � �
�� �� �
the relative loss in the received power can vary from 0 dB to 3,9 dB depending on the RIS position (relative to Tx and
Rx).
4.2 Metasurface designs
RISs are composed of certain arrangement controllable resonators (unit-cells). These unit-cells can be implemented
based on the deployment scenarios and requirements. For instance, in the Frequency Range 1 (FR1) regime they are
typically metallic patches stacked on top of a dielectric. If the unit-cells are in the scale of subwavelength, they will
form a composite called metasurface. The subwavelength granularity of these unit-cells confers metasurfaces with
exceptional control of EM waves, that can even realize some unnatural EM properties such as negative permittivity (� )
�
or permeability (� ). With this feature, EM characteristics of impinging waves can be engineered.
�
One of the many challenges posed by this approach concerns the design and development of metasurfaces. This task is
largely hindered by the unique combination of resource constraints and communication requirements of this new
networking scenario, which prevents the use of conventional techniques and requires radically new solutions instead.
The performance of RIS metasurface depends on the size of the unit-cells, the number of unit-cell states, and its overall
size. On the other hand, there are costs and energy overheads associated with the fabrication and operation of
metasurfaces that also scale with the aforementioned factors. Hence, to build an RIS capable of satisfying a set of
application-specific requirements with the minimum cost, it becomes necessary to quantify the main scaling trends and
trade-offs of the underlying metasurface design.
4.3 Switching element
RIS reconfiguration can be achieved through element inclusion (PIN diodes, varactors, etc.) within unit-cells. The
tuning factor can be applied to unit-cells individually and to select the unit-cell state (each unit-cell can acquire different
state from a selective number of states � ). The tuning factor can be used for frequency tuning or function adjustment.
�
ETSI
10 ETSI GR RIS 004 V1.1.1 (2025-03)
Realization of reconfigurable metasurfaces requires a network of wires or vias to convey the command signal from the
control unit (i.e. RIS controller) to the surface.
The intensity and phase of reflecting EM waves are controlled by the variation of impedance � in the unit cells
�
through the switching element inclusion (PIN diodes, varactors, etc.). The conductive layer of the RIS can be described
as a penetrable equivalent impedance surface Z, which relates the tangential electric field � to the discontinuity of the
�
average tangential magnetic field � across the conductive layer. The incident EM plane wave is characterized in terms
�
of transverse wavenumber � and the periodicity of RIS elements along the impedance profile �:
��
���
�� �
� � ∑ �
� � = � �
� �
Then, the Floquet waves expansion of the currents induced in the equivalent impedance boundary in the �� direction can
be expressed as:
��� �
��
������ = � × � = ∑ � � ��
� � �
��
where the Floquet wavenumbers are defined as � = � + �,
�� ��
�
�
m is a constant denoting the number of unit cells, and n represents individual reflecting coefficients for propagating
diffracting harmonics of index � = 0,∓1,∓2,… . The sum of n-induced currents on the equivalent impedance boundary
provides the accurate description of RIS, with the dispersion characteristics given in terms of frequency dispersion
diagrams showing the transverse wavenumber as a function of the propagation direction for different frequencies. This
relationship is illustrated in Figure 4.3-1.

Figure 4.3-1: RIS modeled as an impedance boundary characterized by a transverse wavenumber !
!
RIS can be realized by using various phase switching methods, where each method has its own advantages and
disadvantages as summarized in Table 5.3.1-1 of ETSI GR RIS 002 [i.2]. As outlined in the table, the selection of the
switching element is typically based on the following:
• Frequency of operation
• Switching speed
• Power consumption
• Insertion loss
• Size
• Cost
ETSI
11 ETSI GR RIS 004 V1.1.1 (2025-03)
Out of the items outlined, only varactor diodes and liquid crystals can provide continuous phase switching as a function
of the applied voltage that is typically regulated with Digital to Analogue Converters (DACs). This method of control is
called "Analogue" because any phase value can be realized on such RIS. Other phase switching methods such as PIN
diodes can only represent the value of 0 or 1, and this method is called "1-bit Digital", because only the pre-defined
phase values can be realized on such RIS. However, if one unit cell features several switching elements, an "N-bit
Digital" switching method can be realized, where N corresponds to the amount of switching elements within the unit
cell. The design process of multi-bit digital RISs becomes progressively more complex with the amount of added
switching elements. Additionally, this increases the number of control signals from the RIS controller.
The switching speed of unit cell elements needs to be fast enough to realize Time Division Duplexing (TDD)
framework for operation in multi-user environments, which is described in clause 7.2.1 of ETSI GR RIS 002 [i.2]. For
varactor diodes, PIN diodes and FETs it is typically in the region of nanoseconds, but the switching speed of liquid
crystals and MEMS switches is in the region of milliseconds.
Although varactor diodes have negligible power consumption across the diode itself (< 1 mW), their application in
analogue mode requires the use of DACs and operational amplifiers, which increases the overall power consumption of
such RIS. Multiple unit cells can share the same control channel on an analogue RIS, for example in a diagonal RIS
each column can be driven by a single DAC channel. However, this restricts beam steering to a single plane.
In case of a digital RIS, PIN diodes have higher power consumption across the diode itself (~5 mW) but can be driven
directly from the microcontroller with CMOS logic. Digital RIS can also be implemented with multiple varactor diodes
on the same unit cell that are switching between two or more voltage levels, but it requires the addition of voltage
boosters and increases complexity of the unit cell design.
Most base stations are equipped with orthogonal and dual-polarized antenna arrays and most mobile user terminals are
integrated with impurely polarized internal antennas. Hence, the unit cells of a RIS array should be designed with dual-
polarization functionality in order to control any incoming EM wave with a random polarization successfully. The
described scenarios below illustrate two RIS examples for the single- and dual-polarization RIS configurations,
respectively. As shown in Figure 4.3-2, when the RIS design is specific to supporting merely one polarization
orientation, only the polarized incident signals fit for the designed polarization are able to enhance the beamforming
gain, whereas those whose polarization is orthogonal to the designed one cannot see any EM-field reconfigurability. By
contrast, if a dual-polarized RIS is deployed instead, as shown in Figure 4.3-3, it will gain considerable advantage such
that the orthogonally polarized signals simultaneously showcase an improvement in focusing the reflected waves on an
aimed direction. This holds effective too when the EM-fields rotate by some inclination angle, which is further set forth
in Figure 4.3-4 and Figure 4.3-5. Suppose that the radio wave groups propagate towards a unipolarised RIS at an
incident angle of either 45 degrees or -45 degrees in Figure 4.3-3, both the radio wave groups of orthogonal
polarizations sustain a roughly 3 dB polarization mismatch loss as compared to a dual-polarized RIS in Figure 4.3-5.
To support dual-polarized unit cell design for a RIS, it may need to integrate more than one phase switching elements
for phase control of the incoming orthogonally polarized EM waves. On the other hand, this may increase the overall
power consumption and the complexity of control signalling and circuit designs.
ETSI
12 ETSI GR RIS 004 V1.1.1 (2025-03)

Figure 4.3-2: Scenarios of orthogonally polarized EM waves impinging on a RIS
which only support specific polarization control and their corresponding radiation characteristics

Figure 4.3-3: Scenarios of orthogonally polarized EM waves impinging on a RIS
which fully support dual polarization control and their corresponding radiation characteristics

ETSI
13 ETSI GR RIS 004 V1.1.1 (2025-03)

Figure 4.3-4: Unipolarised RIS illumination scenarios and radiation characteristics of orthogonally
polarized EM waves impinging on a RIS at a slant angle
of 45 degrees and -45 degrees with respect to the RIS arrangement

Figure 4.3-5: Dual-polarized RIS illumination scenarios and radiation characteristics of orthogonally
polarized EM waves impinging on a RIS at a slant angle
of 45 degrees and -45 degrees with respect to the RIS arrangement
ETSI
14 ETSI GR RIS 004 V1.1.1 (2025-03)
4.4 RIS controller
Critical design aspects for RIS controller typically include:
• Power consumption
• Switching speed
• Cost
The selection of electronic components will vary depending on the phase switching mode, which could be either
analogue or digital. The power consumption of the RIS controller is largely shaped by the number of required control
lines and GPIO pins, which drastically increases in case of 2-Dimensional beam steering mode of operation. Digital
logic expanders and transistor switching matrices can be used to reduce the number of utilized GPIO pins on the
microcontroller/FPGA, but inevitably they add to the total system delay, which can be expressed as follows:
� �
� �� �� �� � ∑ � � ∑ �
� �� ��� ��� ��� � ��� �
where � is the switching delay of the unit cell switching element, � is the microcontroller time delay that includes
�� ���
� is the time delay of the DAC in case of analogue switching method, M indicates the number of
the rise/fall time,
���
logic elements in the chain, � is the time delay of each additional logic gate in the chain and � is the propagation
� �
delay for each path in the dielectric material.
It can be experimentally shown that the total system delay is largely dominated by the � in an analogue RIS,
���
therefore a digital RIS has the benefit of faster switching speed. However, the actual requirement for � will be dictated
�
by the operational environment, which is subject to the 5G NR frame structure. This requirement can be calculated
based on the Subcarrier Spacings (SCSs) specified in Table 5.3.2-1 of ETSI TS 138 101-1 [i.7], which are different for
FR1 and FR2. For example, in a downlink dominated scenario, the entire Channel State Information (CSI) from the UE
could be contained within a single time slot. Assuming FR1 frequency band and 15 kHz SCS, the � should be less than
�
1 ms to prevent packet loss during UE movement.
4.5 RIS interfaces
The RIS as a whole can be modelled as the combination of RIS controller and RIS panel (see Figure 4.5-1). The RIS
panel comprises a group of elements, which can reflect, refract, or absorb incident radio waves. The various types of
RIS will be detailed in later clauses of the present document. The RIS controller refers to a component of RIS,
responsible for configuring the RIS elements to achieve a wanted way of manipulating the incident radio wave,
potentially processing any signalling received from another network node. The configuration of the RIS element by the
microcontroller is conveyed through control signalling from the RIS controller. Inside RIS, one interface is the interface
between the RIS microcontroller and RIS panel to transmit the control signals.

Figure 4.5-1: Illustration of a RIS comprising a RIS controller and a RIS panel
Integration of RIS into the network facilitates various applications, extending beyond the coverage-focused roles of
integrated access and backhaul and network-controlled repeaters. The RIS multi-functionality allows the use range to
expand from improving coverage to enabling wireless power transfer, supporting ambient backscatter communications,
enhancing positioning accuracy, and strengthening secure communication.
ETSI
15 ETSI GR RIS 004 V1.1.1 (2025-03)
RIS controlling strategies may include BS/AP-controlled (through one or more BS/AP) and UE-controlled (one or more
UEs), see Figure 4.5-2. This illustration follows closely the methods of controlling RIS that have been previously
detailed in ETSI GR RIS 002 [i.2].
Control link Control link
RIS Controller
RIS-aided DL
BS/AP UE
RIS Panel
RIS-aided UL
Figure 4.5-2: RIS architecture where RIS is configured from the BS/AP or UE using control signalling
In the downlink (e.g. BS/AP-controlled RIS), the control information can be transmitted from the BS to the RIS via the
air interface, such as the Physical Downlink Control Channel (PDCCH) or the Physical Downlink Shared Channel
(PDSCH) in the 5G NR architecture. In the uplink (e.g. UE-controlled RIS), the control information can be transmitted
from the UE to the RIS via a direct communication interface, such as the Physical Sidelink Control Channel (PSCCH)
or Physical Sidelink Shared Channel (PSSCH) in the 5G NR architecture. Moreover, for a RIS with UL transmission
capability, the feedback information (e.g. ACK-NACK) for the received control information can be transmitted from
the RIS to the BS via the air interface or transmitted from the RIS to the UE via a direct communication interface.
The application of back-scattering communication via digital coding on RIS and the meta-cryptography proposed in
[i.17] may be also considered. Encoded patterns may be transferred between various network devices over short
distances, allowing continuous network probing and authentication, as well as a secure RIS configuration data transfer.
Therefore, increasing the overall security of the network and allowing it to dynamically configure RIS.
4.6 RIS power source
When considering the power source requirements for RIS, the power consumption evaluation of all components of the
RIS is needed. Typically, for a passive RIS, the following components are considered:
• RIS controller/interface: RIS controller is responsible for processing any control information that it may
receive from the controlling node. Power consumption of the RIS controller primarily depends on the
frequency of control information, i.e. how frequent the control information is received for updating the RIS
configuration. The processed information is then applied to the unit cells via the RIS interface that generates
the required voltage/current to adjust the state of the switching elements for changing properties of the
metamaterial.
• RIS unit cells: Power consumption of the unit cells depends on factors including the type of switching
elements to change the state of unit cells, number of unit cells, bit resolution for phase shifts and polarization
mode i.e. single or dual polarization. As described in clause 4.3, there can be different types of switching
elements and the selection of particular switching element is dependent on a number of factors including
power consumption.
For illustration, the total power consumption for a PIN diode based RIS can be determined as follows (considering each
unit cell has a dedicated set of PIN diodes as switching elements):
� = � + �
�"��� �"���"�/�����#��� �����$�#���,
where:
� �� "ℎ� #�$�% %�&’�%�� (�% %����)��� *�� #%�������� ��(�%+*"��� *" ���"%����%
�"���"�/�����#���
% � &
�,�,�
� = , , ,�
�����$�#��� $��������
- = �’+.�% �( %�$� �( ’��" �����
� = �’+.�% �( ���’+�� �( ’��" �����
ETSI
16 ETSI GR RIS 004 V1.1.1 (2025-03)
� � 1 �� 2, ��� ������ �� ���� ������������ ����
�� �� �
�,�,� �,�,�
�,�,�
��
� �� �
��������� �����
� � ������ �� ��� ������ ��������� �� ���� ���� �� ��� "�",������ "�" & ��� ������������ "�"
�,�,�
� � ������ �� ��� ������ ��������� �� ���� ���� �ℎ�� ℎ� � "!""" ����� & ���′� ��$���� �����
�,�,�
� % � � ������ �� ��� ������ ��������� �� ���� ���� �ℎ�� ℎ� � "!�" ����� & ��$���� �����
�,�,� �,�,�
��
� � ����� ��$����� ��� � ��� ����� �� "!�" �����
�����
For RIS with other switching elements, the power consumption may be calculated differently, depending on the number
of switching elements may be required for achieving same level of phase quantization.
Existing RIS prototypes are powered by traditional means such as the Mains electrical grid, Power over Ethernet (PoE)
or Direct Current (DC). In general terms, the power consumption of RIS can be expressed as:
� �
� ��
� �� &� � &
��� ���_�� � ��_��
�
��
where � is the number of unit cells, � is the static power consumption of the RIS controller, � is the static
� ���_�� ��_��
power consumption of each unit cell, ’ is the frame duration, and ( is the additional energy required to reconfigure
�� ��
each unit cell, which is assumed to be the same for all unit cells. This formulation shows that the rate at which RIS
performs phase updates does not affect the power consumption.
The use of electrical grid or PoE restricts implementation of RISs only to areas with readily available electric power.
Instead, alternative methods for power generation with EH elements placed directly on the metasurface have been
proposed by a) integrating solar cells on RIS or b) recycling Radio Frequency (RF) energy as illustrated in Figure 4.6-1
and Figure 4.6-2.
Figure 4.6-1: Integration of multi-junction solar cells on RIS operating in the FR1
a) A metasurface with interleaving solar cells and reflective unit cells
b) A unit cell with combined solar and RF elements, where W is the width of solar cell and
g is the gap between solar cell and RF element
ETSI
17 ETSI GR RIS 004 V1.1.1 (2025-03)

Figure 4.6-2: Integration of RF energy harvesting on RIS in a hybrid operation where a part
of radio signal is absorbed to generate power and maintain the RIS operation
Energy harvesting can be performed separately from phase optimization and the amount of harvested energy in DC at a
specific time slot can be expressed as:
� �
��� ���
�
��
���� �� ����
���
�� �
���
� )Α +�
�
� !
" �
��
���
) +
where � , is the harvested power that is received by the DC rectifier, � is a constant denoting the maximum
�# ! �$%
harvested power when the harvesting circuit at the
...