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Reconfigurable, Intelligent, and SustainableWireless Environments for 6G Smart Connectivity
Emilio Calvanese Strinati, George C. Alexandropoulos, Henk Wymeersch, Benoit Denis, Vincenzo Sciancalepore, Raffaele D'Errico, Antonio Clemente, Dinh-Thuy Phan-Huy, Elisabeth De Carvalho, Petar Popovski
TL;DR
Future 6G networks need flexible connectivity for heterogeneous applications, regulations, and localized requirements, but conventional designs treat the wireless environment as uncontrolled. This paper proposes RISE, combining RISs with network infrastructure to introduce WEaaS and spatially focused PBAs, and discusses their architectures, O-RAN integration, and challenges. The paper describes PBAs for localized data rates, localization, radio mapping, low EMF, energy efficiency, and secrecy, while identifying realistic propagation models, hardware, integration protocols, and distributed-intelligence methods as open challenges.
Problem
6G must accommodate heterogeneous applications, regulations, and user-, service-, and location-based requirements whose KPIs may need to be delivered locally in space and time.
Method
The paper proposes RISE, combining negligible-power RISs with conventional nodes, and develops the WEaaS and PBA networking concepts.
Results
PBAs are described as localized regions supporting extreme data rates, accurate localization and radio mapping, adaptive EMF exposure, low-energy connectivity, and improved secrecy.
Takeaways & Limitations
RISE frames RISs as a Layer-0 technology for spatially focused, sustainable 6G connectivity integrated with conventional infrastructure and O-RAN.
Abstract
from arXiv · showhide
Various visions on the forthcoming sixth Generation (6G) networks point towards flexible connect-and-compute technologies to support future innovative services and the corresponding use cases. 6G should be capable to accommodate ever-evolving and heterogeneous applications, future regulations, and diverse user-, service-, and location-based requirements. A key element towards building smart and energy sustainable wireless systems beyond 5G is the Reconfigurable Intelligent Surface (RIS), which offers programmable control and shaping of the wireless propagation environment. Capitalizing on this technology potential, in this article we introduce two new concepts: i) wireless environment as a service, which leverages a novel RIS-empowered networking paradigm to trade off diverse, and usually conflicting, connectivity objectives; and ii) performance-boosted areas enabled by RIS-based connectivity, representing competing service provisioning areas that are highly spatially and temporally focused. We discuss the key technological enablers and research challenges with the proposed networking paradigm, and highlight the potential profound role of RISs in the recent Open Radio Access Network (O-RAN) architecture.
I. INTRODUCTION
Beyond-5G research targets flexible 6G connectivity that can adapt to evolving applications, regulations, and localized requirements. RISs provide a hardware-efficient means to control wireless propagation, motivating the RISE paradigm and its WEaaS and PBA concepts.
- 6G research addresses future connect-and-compute needs beyond the single platform provided by still-deploying 5G networks.
- Proposed 6G KPIs include up to 10 Gb/s/m3 capacity, 100 µs latency, 1 Tb/J energy efficiency, and 1 cm 3D localization accuracy.
- These KPIs need not be achieved simultaneously everywhere, but should be delivered flexibly in localized regions and times.
- RISs use hundreds or thousands of nearly passive reconfigurable elements to support functions including relaying, nulling, estimation, detection, beamforming, and multipath shaping.
- RISE combines negligible-power RISs with conventional network nodes to optimize propagation and infrastructure for selective service provisioning.
- WEaaS trades off capacity, energy efficiency, localization accuracy, and secrecy while accommodating spectrum and EMF constraints; PBAs focus these services in space and time.
II. THE RISE NETWORK PARADIGM
RISE integrates multiple spatially distributed, heterogeneous RISs into 5G-and-beyond infrastructure. This reuse supports spatially focused provisioning while reducing expenditure and energy consumption.
- RISE integrates multiple spatially distributed RISs within 5G-and-beyond network components.The RISs may differ in size and low-power hardware technology.
- Reusing mobile network infrastructure can reduce operational and capital expenditure.
- Highly spatially focused service provisioning can lower energy consumption.
A. Core Network Components
RISE adds a programmable Layer-0 smart radio environment of densely deployable RISs beneath conventional wireless Layer-1. Orchestration, AI-assisted control, and multidimensional resource allocation coordinate this environment with legacy infrastructure.
- Layer-0 introduces multiple low-cost, nearly passive RISs as a programmable wireless medium for current and future Layer-1 standards.RISs can be embedded in objects and appliances in scalable cell-free or multi-tenant deployments.
- Edge AI and machine learning are intended to learn resource allocation and support energy efficiency, low EMF, secrecy, and time-constrained services.The same algorithms are intended to provide automated and self-healing orchestration during network changes or failures.
- RIS Control: RISs may be controlled in-band through affected wireless signals or out-of-band through a communication interface decoupled from RIS reconfiguration.In-band control must preserve an operational control channel, whereas out-of-band control separates control from reconfiguration.
- RIS Control: Layer-0 resources allocated to stakeholders may be partitioned by space, time, frequency, or combinations of these dimensions.
C. Performance Benefits
RISE uses low-cost, nearly passive RIS infrastructure to create localized connectivity benefits while reducing installation, maintenance, energy, and control burdens. RIS deployment can target diverse environments and service objectives.
- RISs can be deployed in outdoor, indoor hotspot, public user-dense, residential, and Industry 4.0 settings to boost wireless connectivity.
- Nearly passive and low-cost infrastructure can avoid or alleviate network installation and maintenance requirements compared with additional active hotspots.
- Expected benefits include lower delay, reduced RIS-network energy consumption, wireless rather than high-rate wired RIS control, and lower infrastructure installation effort.The comparison is with conventional transceivers and relays for energy consumption.
III. THE RISE-EMPOWERED CONCEPTS
RISE introduces Smart Radio Environments that use RISs to create highly localized, customized connectivity through Wireless Environment as a Service and Performance-Boosted Areas.
- RISE enables highly localized quality of experience and specific service types by controlling an otherwise imposed wireless medium.
- Performance-Boosted Areas: Performance-Boosted Areas are dynamically designed regions that manipulate radio propagation to meet selected KPIs.
- Performance-Boosted Areas: Rate-, localization-, low-EMF-, energy-efficient-, and secrecy-boosted areas target distinct connectivity, positioning, exposure, energy, and security objectives.
- Wireless Environment as a Service: WEaaS can coordinate service levels and continuity for users inside or outside operator-specific boosted areas according to their locations and needs.
B. Multi-Operator RIS WEaaS
Multi-operator WEaaS lets operators share RIS resources to satisfy location-dependent communication needs, while a shared RIS can outperform individually controlled RISs with lower hardware cost and power consumption.
- Two operators can share pre-deployed RISs either orthogonally by sub-area reservation or non-orthogonally through joint spatial resource allocation.
- The evaluation compares a shared RIS with two individually controlled RISs and with no RIS under Rayleigh fading and random phase configurations.
- The shared-RIS WEaaS case provides substantial link budget gains over individually deployed RISs with half the hardware cost and power consumption.
- A single BS with RIS-assisted multipath localization can dynamically tune the UE location uncertainty region's size and orientation around application requirements.
IV. 6G TECHNOLOGY ENABLERS AND CHALLENGES
The RISE paradigm requires new communication models that jointly represent controllable propagation, information transmission, electromagnetic behavior, and reconfigurable materials, while realistic RIS modeling remains an open challenge.
- RISE shifts communication design from optimizing transmission over a fixed channel toward controlling the propagation channel itself.
- This shift calls for mathematical models combining communication information theory, electromagnetic propagation, and reconfigurable metamaterials.
- Realistic models must capture RIS state changes and propagation effects across near- and far-field regions, including grating lobes and interactions among reflecting RISs.
B. Open and Flexible Network Architecture Design
RISE can extend O-RAN with a controllable RIS-based network segment, new interfaces, and edge orchestration, but practical RIS hardware still faces control, functionality, and fabrication challenges.
- Open and Flexible Network Architecture Design: RISE components can integrate with O-RAN through NFV/MANO, adding a network segment between RAN elements and UEs.
- Open and Flexible Network Architecture Design: The RISE controller can command RIS elements on millisecond timescales and receive longer-timescale transmitter configurations through the Rx reference point.
- Open and Flexible Network Architecture Design: The proposed O-RAN integration introduces Rx and R2 interfaces while leaving the RU–RIS interface open.
- Multi-Functional RIS Hardware: RISs use nearly passive switching and phase-manipulation units, but simultaneous multi-function control and complete polarization control remain unreported or partial.
- Multi-Functional RIS Hardware: Dynamic RIS control still has complicated cabling, especially at higher frequencies, motivating fabrication methods spanning sub-6 GHz, mmWave, and sub-THz bands.
D. RIS Integration Protocols
RIS integration requires protocols that coordinate RIS control, augmented radio resources, and interactions with legacy network infrastructure. Channel acquisition and tracking remains a central challenge, especially for passive RISs and mobile users.
- Novel RIS integration protocols must orchestrate RIS control, allocate augmented radio resources, and connect RISs with legacy network infrastructure.
- Channel Acquisition and Tracking uses passive-RIS receiver protocols or RIS sensing and AI techniques, depending on RIS hardware capabilities.Passive approaches use activation patterns or angular-domain compressed sensing; equipped RISs can use AI-based CAT.
- Passive-RIS CAT requires dedicated channel sensing and estimation protocols operated by conventional receivers.
- Reducing CAT overhead is especially important with mobile UEs, while sensor-equipped RIS research remains exploratory and immature.The passage identifies training duration and control signaling as key overheads.
E. Multi-Access Edge Computing and Learning
RIS-enabled networking is positioned to extend edge computing beyond static offloading by supporting adaptation, reliability, localization, and distributed intelligence. The proposed paradigm combines proactive resource provisioning with sensing and learning for focused connectivity services.
- Multi-Access Edge Computing and Learning: MEC brings cloud functionalities to the wireless edge, where computation offloading can save device energy or support sophisticated low-latency applications.
- Multi-Access Edge Computing and Learning: Existing RIS-assisted offloading schemes target the MEC energy-latency trade-off but address only static computation-offloading problems.
- Multi-Access Edge Computing and Learning: The WEaaS-enabled RISE paradigm targets fiber-like connectivity and reliability through proactive resource provisioning and backup links from multiple RISs.This is intended to support intermittent blockage conditions and mobile edge services.
- Environment Awareness and Distributed Intelligence: PBA-based connectivity requires accurate, timely UE locations and propagation conditions to control RISs effectively.
- Environment Awareness and Distributed Intelligence: Localization-oriented control should jointly operate at RIS and system levels using directional RIS operation, channel reconfigurability, and advanced processing.Suggested tools include decentralized or federated machine learning and multi-objective optimization.
- Environment Awareness and Distributed Intelligence: RISE proposes distributed situational awareness and intelligence to learn mobility patterns and support proactive protocol decisions for focused service areas.
V. RESEARCH ROADMAP AND CONCLUSION
The RISE view proposes RIS-enabled wireless environments as a new 6G connectivity paradigm centered on WEaaS and spatiotemporally focused PBAs. It outlines channel, network, sensing, sustainability, and architectural challenges for realizing this vision.
- The RISE view introduces WEaaS and spatiotemporally focused performance-boosted areas as two central concepts for future 6G wireless connectivity.
- The roadmap calls for realistic channel models that harmonize RIS-based and conventional electromagnetic-wave propagation.
- It discusses fundamental limits spanning connectivity, localization, sensing, and sustainability in RIS-empowered networks.
- The proposed mechanisms combine multiple RIS control channels with channel-estimation and sensing schemes supporting capacity, energy efficiency, controlled EMF exposure, and tunable localization accuracy.
- Energy-sustainable RIS hardware and architectural integration are identified as part of the RISE research agenda.