Channel Orthogonalization With Reconfigurable Surfaces : General Models, Theoretical Limits, and Effective Configuration
Alegria, Juan Vidal LU
; Thunberg, Johan
LU
and Edfors, Ove
LU
(2025)
In IEEE Transactions on Wireless Communications
24(6).
p.5179-5195
- Abstract
We envision a future in which multi-antenna technology effectively exploits the spatial domain as a set of non-interfering orthogonal resources, allowing for flexible resource allocation and efficient modulation/demodulation. We may refer to this paradigm as orthogonal space-division multiplexing (OSDM). On the other hand, reconfigurable intelligent surface (RIS) has emerged as a promising technology which allows shaping the propagation environment for improved performance. This paper studies the ability of three extended types of reconfigurable surface (RS), including the recently proposed beyond diagonal RIS (BD-RIS), to achieve perfectly orthogonal channels in a general multi-user multiple-input multiple-output (MU-MIMO) scenario. We... (More)
We envision a future in which multi-antenna technology effectively exploits the spatial domain as a set of non-interfering orthogonal resources, allowing for flexible resource allocation and efficient modulation/demodulation. We may refer to this paradigm as orthogonal space-division multiplexing (OSDM). On the other hand, reconfigurable intelligent surface (RIS) has emerged as a promising technology which allows shaping the propagation environment for improved performance. This paper studies the ability of three extended types of reconfigurable surface (RS), including the recently proposed beyond diagonal RIS (BD-RIS), to achieve perfectly orthogonal channels in a general multi-user multiple-input multiple-output (MU-MIMO) scenario. We consider practical implementations for the three types of RS consisting of passive components, and obtain the corresponding restrictions on their reconfigurability. We then use these restrictions to derive closed-form conditions and explicit expressions for achieving arbitrary (orthogonal) channels. We also study the problem of exploiting the degrees of freedom (DoFs) from the channel orthogonality constraint to maximize the channel gain while maintaining the passive RS constraints, and we propose some initial methods with satisfying performance. Finally, we provide some channel estimation and RS configuration techniques within this framework, where the computations are assumed to be performed at the BS, and we derive some limits on the amount of overhead required to achieve channel orthogonalization with RSs. The numerical results confirm the theoretical findings, showing that channel orthogonality with passive RSs can be effectively achieved in practical environments as long as the direct channel is not significant with respect to the RS cascaded channel. We thus take some important steps towards realizing OSDM.
(Less)
- author
- Alegria, Juan Vidal
LU
; Thunberg, Johan
LU
and Edfors, Ove
LU
- organization
- publishing date
- 2025
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- beyond diagonal reconfigurable intelligent surface (BD-RIS), channel orthogonalization, MU-MIMO, orthogonal spatial domain multiplexing (OSDM), Reconfigurable surface (RS)
- in
- IEEE Transactions on Wireless Communications
- volume
- 24
- issue
- 6
- pages
- 17 pages
- publisher
- IEEE - Institute of Electrical and Electronics Engineers Inc.
- external identifiers
-
- scopus:86000466940
- ISSN
- 1536-1276
- DOI
- 10.1109/TWC.2025.3546429
- language
- English
- LU publication?
- yes
- id
- e556c96f-51c0-42eb-82ec-0c92e59b8b17
- date added to LUP
- 2025-06-26 08:08:13
- date last changed
- 2025-06-26 08:08:52
@article{e556c96f-51c0-42eb-82ec-0c92e59b8b17,
abstract = {{<p>We envision a future in which multi-antenna technology effectively exploits the spatial domain as a set of non-interfering orthogonal resources, allowing for flexible resource allocation and efficient modulation/demodulation. We may refer to this paradigm as orthogonal space-division multiplexing (OSDM). On the other hand, reconfigurable intelligent surface (RIS) has emerged as a promising technology which allows shaping the propagation environment for improved performance. This paper studies the ability of three extended types of reconfigurable surface (RS), including the recently proposed beyond diagonal RIS (BD-RIS), to achieve perfectly orthogonal channels in a general multi-user multiple-input multiple-output (MU-MIMO) scenario. We consider practical implementations for the three types of RS consisting of passive components, and obtain the corresponding restrictions on their reconfigurability. We then use these restrictions to derive closed-form conditions and explicit expressions for achieving arbitrary (orthogonal) channels. We also study the problem of exploiting the degrees of freedom (DoFs) from the channel orthogonality constraint to maximize the channel gain while maintaining the passive RS constraints, and we propose some initial methods with satisfying performance. Finally, we provide some channel estimation and RS configuration techniques within this framework, where the computations are assumed to be performed at the BS, and we derive some limits on the amount of overhead required to achieve channel orthogonalization with RSs. The numerical results confirm the theoretical findings, showing that channel orthogonality with passive RSs can be effectively achieved in practical environments as long as the direct channel is not significant with respect to the RS cascaded channel. We thus take some important steps towards realizing OSDM.</p>}},
author = {{Alegria, Juan Vidal and Thunberg, Johan and Edfors, Ove}},
issn = {{1536-1276}},
keywords = {{beyond diagonal reconfigurable intelligent surface (BD-RIS); channel orthogonalization; MU-MIMO; orthogonal spatial domain multiplexing (OSDM); Reconfigurable surface (RS)}},
language = {{eng}},
number = {{6}},
pages = {{5179--5195}},
publisher = {{IEEE - Institute of Electrical and Electronics Engineers Inc.}},
series = {{IEEE Transactions on Wireless Communications}},
title = {{Channel Orthogonalization With Reconfigurable Surfaces : General Models, Theoretical Limits, and Effective Configuration}},
url = {{http://dx.doi.org/10.1109/TWC.2025.3546429}},
doi = {{10.1109/TWC.2025.3546429}},
volume = {{24}},
year = {{2025}},
}