Source-linked AI summary
RIS-Enabled Integrated Access and Relay: Empowering Collaboration Among BSs
Hao Lin, Mustafa A. Kishk, Mohamed-Slim Alouini
TL;DR
Uneven IoT traffic can leave some BSs heavily loaded while others are idle, motivating better coordination between them. The paper proposes co-sited RISs as part of an IAR architecture and reports coverage improvements in cellular and cell-free networks, while identifying adaptive resource management as a challenge.
Problem
Uneven IoT distributions can leave some BSs heavily loaded and others idle, limiting use of network spectrum and computation resources.
Source: B. Advantages of IAR · p. 2Method
The paper equips BSs with co-sited RISs to form IAR BSs that redirect access requests and support BS cooperation.
Source: A. Operational Mechanism of IAR · p. 1Results
IAR improves coverage in cellular and cell-free networks; in the cellular dynamic-sub-carrier case, coverage improves by 18% at SINRth = 1 and Nm = 1.
Source: C. IAR-empowered cell-free network · pp. 4–5, D. IAR-empowered cellular network · p. 5, CONCLUSION · p. 7Takeaways & Limitations
IAR offers a way for BSs to collaborate through signal redirection, with reported coverage gains across cellular and cell-free settings.
Source: CONCLUSION · p. 7IAR requires adaptive resource management that plans spectrum, user beams, and RIS elements and phase control as traffic and device locations change.
Source: OPPORTUNITIES AND CHALLENGES · p. 6
Abstract
from arXiv · showhide
The increasing number of Internet of Things (IoT) devices and applications leads to severe access congestion in conventional base station (BS) networks. Meanwhile, the low transmit power of IoT devices requires larger diversity gains from the system design. Therefore, low-cost traffic management and signal enhancement mechanisms become essential. Reconfigurable intelligent surfaces (RISs) are increasingly significant due to their flexibility and efficiency. Using reflection, refraction, and amplification, RISs can act as innovative relay nodes to overcome spatial limitations caused by blockages, and improve the coverage range of existing infrastructure. However, more extensive applications of RISs remain to be explored. In this paper, we propose to deploy co-sited RISs on BSs and use the integrated access and relay (IAR) architecture to enable wave-domain task-offloading between BSs, without requiring extra infrastructure or incurring extra decoding latency. Considering the fixed and dynamic sub-carrier schemes, we show the performance improvement in cell-free networks and cellular networks. In addition, we investigate the effect of RIS elements allocated to each IoT device in both cell-free and cellular networks. Finally, we discuss the opportunities and challenges of IAR BSs for future communications design.
A. Operational Mechanism of IAR
IAR BSs use co-sited RISs to redirect IoT requests from direct to indirect BS links, coordinating access and relay roles. Fixed RIS sub-arrays, shared BS load information, and triggered reconfiguration support the links while managing interference and overhead.
A. Operational Mechanism of IAR
- When RIS components are inactive, IAR reduces to a conventional network without extra signaling; active components provide reflection-based diversity but add signaling overhead.The paper assumes configuration overhead and latency are acceptable when establishing the RIS-assisted link.Source: A. Operational Mechanism of IAR · p. 1
- Each redirection uses one fixed-size RIS sub-array with phases optimized for the target device; reconfiguration is triggered by movement, shadowing, BS failures, or system updates.Phase control seeks to strengthen and direct the serving signal while limiting interference from other devices.Source: A. Operational Mechanism of IAR · p. 2
- A BS acts as an access node when its direct link has resources, a relay node when it redirects traffic, or an IAR node when cell-free devices use both paths.If RIS elements or frequency resources are busy or broken, Mode 3 reduces to Mode 1 or Mode 2.Source: A. Operational Mechanism of IAR · p. 2
- Timely BS load sharing narrows candidate iLoS links and reduces matching complexity, but coordination periods must balance signaling overhead against stale load information.The paper allows centralized coordination for small or compute-rich networks and distributed coordination for large or compute-limited deployments.Source: A. Operational Mechanism of IAR · p. 2
B. Advantages of IAR
IAR equips BSs with co-sited RISs to redirect traffic and provide additional paths, offering deployment compatibility, offloading, and diversity benefits. Its access schemes trade frequency flexibility and interference against device coverage, while RIS allocation and coordination affect performance and complexity.
B. Advantages of IAR
- Integrating RISs into BSs supports quick deployment without modifying the air interface or framework.The architecture reshapes signal propagation direction and avoids modifying unauthorized buildings.Source: B. Advantages of IAR · p. 2
- Coordinating neighboring BSs can redirect requests from heavily loaded areas to less-loaded BSs, while timely operational-status sharing supports scalable access management.The paper also describes offline routing tables and updating redirection candidates when devices or BSs change.Source: B. Advantages of IAR · pp. 2–3
- RIS-assisted iLoS paths can improve diversity and coverage for suburban devices lacking multiple neighboring dLoS BSs, while increasing the potential burden on the network.The paper contrasts IAR-assisted links with simple load-aware cooperation and notes that narrowband reflections are approximated as frequency-flat.Source: B. Advantages of IAR · p. 3
- RIS allocation balances per-link reflection gain against interference: increasing the number of relay services per BS reduces reflection gain per link, and stronger amplification can intensify interference.The paper uses Monte Carlo simulations in a 1 km × 1 km suburban area to compare IAR and conventional BS coverage probabilities.Source: USE CASES OF IAR BSS · p. 3, PROOF OF CONCEPT AND SIMULATION RESULTS · p. 4
- Fixed sub-carriers avoid device frequency switching but may send devices farther to find service; dynamic sub-carriers use open resources near the device but require frequency adjustment.Both schemes allow resource blocks to serve multiple devices or a single device.Source: USE CASES OF IAR BSS · pp. 3–4
- Multi-device access can serve more users when the SINR threshold is low but introduces interference, whereas single-device access reduces interference but can leave dense-area devices unserved.Multi-device access caps the number of simultaneous users per resource block at Nm.Source: USE CASES OF IAR BSS · p. 4
- Cellular one-hop relaying redirects a failed direct access to a neighboring BS with an open resource block; cell-free relaying attempts the iLoS path even when the dLoS BS is busy.Both approaches try the device's second-closest dLoS BS if the initial paths are unavailable.Source: USE CASES OF IAR BSS · p. 4
C. IAR-empowered cell-free network
In cell-free networks, optimal RIS allocation balances stronger iLoS links against interference. Dynamic sub-carrier access generally improves coverage over fixed access, but its resource blocks should not admit too many devices.
C. IAR-empowered cell-free network
- Coverage generally rises for M<4 as RIS reflections strengthen signals and support diversity branches, then falls for M>32 as reflections increase interference.Coverage improves slightly as M approaches Mtot, when the number of strong interfering iLoS paths decreases.Source: C. IAR-empowered cell-free network · pp. 4–5
- For Nm=2, optimal M=4; for Nm=5, optimal M=16, and optimally allocated IAR cell-free networks outperform C-BSs.The coverage measure counts devices whose maximum SINR at connected BSs exceeds SINRth, using selection combining.Source: C. IAR-empowered cell-free network · pp. 4–5, Figure 3 · p. 5
- Dynamic sub-carrier coverage is generally better than fixed across Nm and M, but optimal performance decreases as more IoT devices share each resource block.With fixed sub-carriers, allowing multiple devices to share a resource can enhance link management; with dynamic selection, each resource block should not allow too many devices.Source: Figure 4 · p. 5, C. IAR-empowered cell-free network · p. 5
- With dynamic access, coverage rises as M increases below 16 but is lower above 16, as added reflection interference and fewer iLoS paths reduce service.For M<16, more RIS elements per reflection help iLoS links decode; above 16, links are already decodable and further increases cause interference.Source: C. IAR-empowered cell-free network · p. 5
D. IAR-empowered cellular network
In cellular networks using dynamic sub-carriers, IAR improves coverage, with gains depending on SINR threshold, relay load, and RIS-element allocation. The section also identifies hardware, interference, and coordination constraints on practical deployment.
D. IAR-empowered cellular network
- Coverage probability improves around 2% at SINR threshold 0.1 with Nm = 1; at SINRth = 1, gains are 18% with Nm = 1 and 12% with Nm = 5.The reported network-wide improvement uses 15 groups of co-sited RIS elements.Source: Figure 5 · p. 5, D. IAR-empowered cellular network · p. 5
- For M > 16, high interference and resource competition occur; at SINR decoding threshold 0.1, increasing Nm from 1 to 5 enables more devices to be successfully decoded and improves coverage.At SINR decoding threshold 1, IAR with Nm = 1 achieves greater coverage enhancement than IAR with Nm = 5 because idle-BS spectral resources can be used more efficiently.Source: D. IAR-empowered cellular network · p. 6
- Monte Carlo simulations show coverage improvements in cellular and cell-free networks, and the authors suggest digital twins to optimize RIS-element pre-allocation for traffic offloading.Dynamic allocation and phase reconfiguration may increase complexity and latency.Source: D. IAR-empowered cellular network · p. 6
- Joint edge and cloud computing could let edge nodes decode interested-device information while reflecting other signals toward the core network.The passage also identifies computing and learning as opportunities to improve IAR security and efficiency.Source: OPPORTUNITIES AND CHALLENGES · p. 6
- Large-scale RIS hardware deployment remains difficult, so affordability and return on investment constrain practical IAR deployment despite requiring components only at BSs.Source: OPPORTUNITIES AND CHALLENGES · p. 6
- IAR BSs may complicate the electromagnetic environment and introduce interference and frequency-resource competition.Source: OPPORTUNITIES AND CHALLENGES · p. 6
- Dynamic traffic requires coordinated spectrum, beam, and RIS control; BS synchronization and RF/phase allocation add computation, motivating lower-latency, lower-overhead cooperation schemes.The burden of RIS reconfiguration is also identified as significant under highly dynamic traffic.Source: OPPORTUNITIES AND CHALLENGES · pp. 6–7
- The paper presents IAR as supporting coverage improvements under both fixed and dynamic sub-carrier schemes, with RIS elements per reflection related to coverage probability.The proposed architecture supports BS collaboration in cellular and cell-free networks.Source: CONCLUSION · p. 7