arXiv subjects

Ertugrul Basar

Publications and source records attributed to Ertugrul Basar.

At least 19 recordsLinked to original sources

arXiv2026

Noise-Domain Non-Orthogonal Multiple Access for Three Users

In this study, we propose a novel three-user noise-domain non-orthogonal multiple access (ND-NOMA) scheme by introducing the correlation as a new dimension besides mean and variance quantities used in two-user ND-NOMA. The new three-user ND-NOMA scheme includes both uplink and downlink scenarios, with detectors designed to decode the information embedded in mean, variance, and correlation. Our theoretical analysis and simulation results under Rician fading channels show that the proposed system is capable of achieving promising bit error rate (BER) performance while preserving the low power and low complexity advantages of ND-NOMA. This new ND-NOMA design enables simultaneous communication among three users using different dimensions, paving the way for scalable multi-user communication in noise-domain systems and in the Internet-of-things (IoT) environments.

cs.IT↗

arXiv2026

A Novel Space-Time Coding Architecture for Rydberg Atomic Quantum Receiver-Based Systems

Rydberg atomic quantum receivers (RAQRs) offer high sensitivity and wide tunability, but their magnitude-based readout yields a nonlinear model incompatible with conventional complex-valued multi-input multi-output (MIMO) processing. We propose a low-complexity space-time coding framework for point-to-point RAQR-assisted MIMO links. Data symbols are encoded using real orthogonal designs, while strong-reference heterodyne reception yields an equivalent real-valued linear model. The preserved orthogonality enables matched filter symbol-wise detection without matrix inversion or vector search. An analytical bit error probability expression is derived, proving the proposed scheme achieves the full transmit-receive diversity. Simulations validate the analysis and demonstrate improved performance over spatial multiplexing benchmarks.

cs.ET↗

arXiv2026

Receive Diversity for Differential Binary Noise Modulation

Differential binary noise (DBN) modulation encodes information in the polarity transition of a reused noise realization, dispensing channel state information and carrier-phase recovery. This letter proposes single-input multiple-output (SIMO) reception for DBN via post-correlation decision-statistic combining, followed by one zero-threshold decision. The combined statistic is a Hermitian quadratic form in complex Gaussian vectors, yielding an exact conditional bit error probability (BEP) with no Gaussian approximation. Averaging it over $κ$-$μ$ fading and the reused energy gives the exact BEP for arbitrary weights. Because that energy is shared, its deep fades are common to every branch, and the observation length caps the diversity order at $\min(Mμ,N)$. The deflection-optimal weights follow in closed form and interpolate soft combining and power weighting. Measured 65 GHz indoor non-line-of-sight (NLoS) results quantify the trade-off between spatial resources and observation length.

eess.SP↗

arXiv2026

CII: Novel CSI-RS Metric for Joint Precoder and RIS Reporting in Multi-User NextG Networks

While reconfigurable intelligent surfaces (RISs) are among the key enablers for next-generation (NextG) wireless networks, efficient feedback reporting for joint base station (BS) precoding and passive RIS configuration remains a major challenge due to the associated signaling overhead. By extending the standard-compliant channel state information reference signal framework, this paper introduces a novel channel information indicator (CII) that jointly represents the active BS precoding matrix and passive RIS configuration within a single feedback metric for multi-user multiple-input single-output systems. Simulation results demonstrate that the proposed unified feedback framework significantly reduces uplink signaling overhead compared with conventional disjoint reporting schemes. Furthermore, despite only a modest increase in the feedback payload, the proposed CII-based scheme outperforms conventional precoding matrix indicator approaches in terms of system performance, offering a practical and standards-compatible solution for RIS integration in NextG wireless networks.

eess.SP↗

arXiv2026

Quantum Meets Statistical-Physical Secrecy: A Novel Hybrid Key Distribution Architecture

This letter proposes a novel hybrid key distribution architecture that jointly exploits quantum key distribution (QKD) and Kirchhoff-law-Johnson-noise (KLJN) statistical-physical key exchange. In the proposed system, an optical BB84-type QKD link operates in coordination with a parallel wired KLJN link, which is used for secure basis handling and, in selected protocols, additional raw key generation. Three novel KLJN-assisted QKD protocols are introduced to eliminate public basis disclosure messages and bit sifting, extract basis-derived key bits, or generate raw key bits under ideal KLJN assumptions. Analytical expressions for the normalized key rate and absolute throughput are derived by accounting for optical channel penalties, KLJN bandwidth constraints, and synchronization bottlenecks. Numerical results show that the proposed hybrid architecture can improve key generation efficiency and throughput in short-haul infrastructures, including metropolitan area networks (MANs) and data center interconnects.

quant-ph↗

arXiv2026

ORIX: Orchestration of RIS with xApps for Smart Wireless Factory Environments

The vision of a smart wireless factory (SWF) demands highly flexible, low-latency, and reliable connectivity that goes beyond conventional wireless solutions. Reconfigurable intelligent surface (RIS)-empowered communications, when integrated with the open radio access network (O-RAN) architectures, have emerged as a promising enabler to meet these challenging requirements. This article introduces the methodology for the orchestration of RIS with xApps (ORIX), bringing the RIS technology into the O-RAN ecosystem through xApp-based control for SWF environments. ORIX features three key components: an O-RAN-compliant RIS service model for dynamic configuration, an RIS channel simulator that supports 3GPP indoor factory models with multiple industrial scenarios, and practical RIS optimization strategies with finite-resolution control. Together, these elements provide a realistic end-to-end emulation platform for evaluating RIS placement, control, and performance in SWF environments prior to deployment. The presented case study demonstrates how ORIX enables the evaluation of achievable performance gains, exploration of trade-offs among key RIS design parameters, and identification of deployment strategies that balance system performance with practical implementation constraints. By bridging theoretical advances with industrial feasibility, ORIX lays the groundwork for RIS-assisted O-RAN networks to power next-generation wireless communication in industrial scenarios.

eess.SP↗

arXiv2026

Gaussian Process-Based Extended Object Estimation for 6G ISAC at Millimeter-Wave Frequencies

This paper introduces a Gaussian process (GP)-based method for extended object estimation (EOE) in integrated sensing and communication (ISAC) scenarios, representing a promising approach to enhance environmental awareness beyond the conventional point-scatterer assumption. The suitability of the proposed GP-based method for EOE is investigated through a practical measurement setup compliant with the fifth-generation (5G) New Radio (NR) standard and employing bistatic sensing, with results evaluated for both mapping and simultaneous localization and mapping (SLAM ) cases at millimeter-wave (mmWave) frequencies. The findings reveal that the enhanced capabilities of communication networks, when combined with bistatic sensing and GP-based EOE, enable improved environmental awareness in future wireless systems. Importantly, the results demonstrate that, under practical conditions, GP effectively performs EOE in both mmWave mapping and SLAM scenarios.

eess.SP↗

arXiv2026

Transceiver-Integrated BD-RIS: Wave-Domain Signal Processing for Sustainable and Inclusive 6G

The shift toward sixth-generation (6G) wireless communications demands transceiver architectures that simultaneously support high-data-rate communications, pervasive sensing, and sub-meter-level localization. Beyond these performance targets, 6G systems are also expected to align with long-term societal goals, including sustainability and inclusiveness. Conventional radio designs, however, remain heavily reliant on digital baseband processing, whose cost, power consumption, and computational complexity scale unfavorably with increasing array size and carrier frequency, making them poorly aligned with these emerging requirements. Beyond-diagonal reconfigurable intelligent surfaces (BD-RISs) introduce a new paradigm by enabling direct manipulation of electromagnetic waves in the analog domain. This article presents BD-RIS as a wave-domain analog processing unit embedded within the transceiver aperture. By migrating linear signal processing functions from the digital baseband to the wave domain, BD-RISs significantly reduce computational load and energy consumption, enabling scalable and sustainable operation for extra-large antenna array systems. Owing to their ability to jointly provide high operational flexibility, modularity, and energy-efficient analog processing, transceiver-integrated BD-RISs offer a compelling architectural trade-off and emerge as a strong candidate for next-generation wireless transceivers.

eess.SY↗

arXiv2026

A Novel CSI-RS Reporting Scheme for RIS Optimization in O-RAN-based NextG Networks

Reconfigurable intelligent surface (RIS) technology is a promising enabler for next-generation (NextG) wireless systems, capable of dynamically shaping the propagation environment. Integrating RIS within the open radio access network (O-RAN) architecture enables flexible and intelligent control of wireless links. However, practical RIS-assisted operation requires efficient acquisition and reporting of channel state information (CSI) to support real-time control from the base station side. This paper proposes a CSI reference signal (CSI-RS)-based reporting scheme for downlink complex channel information (CCI) to facilitate RIS optimization in an O-RAN-compliant environment. The proposed framework establishing CCI extraction and CSI-RS reporting procedures is experimentally validated on a real-world testbed integrating an open-source O-RAN system with an RIS prototype operating in the n78 frequency band. Existing channel estimation-based RIS optimization algorithms, including Hadamard and orthogonal matching pursuit (OMP), are tailored for integration into the O-RAN architecture. Experimental results demonstrate notable improvements in received signal power for both near and far users, highlighting the effectiveness and practical viability of the proposed scheme.

eess.SP↗

arXiv2026

Dual Target-Mounted RISs-Assisted ISAC Against Eavesdropping and Malicious Interference

The synergy between integrated sensing and communication (ISAC) and reconfigurable intelligent surfaces (RISs) unlocks novel applications and advanced services for next-generation wireless networks, yet also introduces new security challenges. In this study, a novel dual target-mounted RISs-assisted ISAC scheme is proposed, where a base station with ISAC capability performs sensing of two unmanned aerial vehicle (UAV) targets, one of which is legitimate and the other is eavesdropper, while communicating with the users through an RIS mounted on the legitimate UAV target. The proposed scheme addresses dual security threats posed by a hostile UAV target: eavesdropping on legitimate user communications and random interference attacks launched by a malicious RIS mounted on this eavesdropper UAV target, aiming to disrupt secure transmissions. Moreover, malicious RIS interference is also optimized for a worst-case scenario, in which both the channel state information (CSI) and the transmit beamforming of the base station are assumed to be fully compromised by a malicious RIS-mounted eavesdropper UAV. A non-convex optimization problem maximizing the secrecy rate of the users is formulated, and a semi-definite relaxation (SDR)-based two-stage solution is developed to optimize the transmit beamforming matrix of the base station and the phase shift coefficients of the legitimate RIS. Extensive computer simulations are conducted to evaluate the robustness of the proposed solution under various system configurations. The proposed system's communication performance is assessed using the secrecy rate metric, while the sensing performance is evaluated through the signal-to-interference-plus-noise ratio and the Cramer-Rao bound (CRB) for angle-of-departure (AoD) estimation of the eavesdropper UAV target.

eess.SP↗

arXiv2025

A Comprehensive Survey of Channel Estimation Techniques for OTFS in 6G and Beyond Wireless Networks

Orthogonal time-frequency space (OTFS) modulation has emerged as a powerful wireless communication technology that is specifically designed to address the challenges of high-mobility scenarios and significant Doppler effects. Unlike conventional modulation schemes that operate in the time-frequency (TF) domain, OTFS projects signals to the delay-Doppler (DD) domain, where wireless channels exhibit sparse and quasi-static characteristics. This fundamental transformation enables superior channel estimation (CE) performance in challenging propagation environments characterized by high-mobility, severe multipath effects, and rapidly time-varying channel conditions. This article provides a systematic examination of CE techniques for OTFS systems, covering the extensive research landscape from foundational methods to cutting-edge approaches. We present a detailed analysis of DD and TF domain CE techniques presented in the literature, including separate pilot, embedded pilot, and superimposed pilot approaches. The article encompasses various algorithmic frameworks including Bayesian learning, matching pursuit-based techniques, message passing algorithms, deep learning (DL)-based methods, and recent CE approaches. Additionally, we explore joint CE and signal detection (SD) strategies, the integration of OTFS with next-generation wireless systems including massive multiple-input multiple-output (MIMO), millimeter wave (mmWave) communications, reconfigurable intelligent surfaces (RISs), and integrated sensing and communication (ISAC) systems. Critical implementation challenges are presented, including leakage suppression, inter-Doppler interference mitigation, impulsive noise handling, signaling overhead reduction, guard space requirements, peak-to-average power ratio (PAPR) management, beam squint effects, and hardware impairments.

eess.SP↗

arXiv2025

Reconfigurable Intelligent Surface Deployments for Mars: Communication and Localization Across Diverse Terrains

Space exploration has witnessed a steady increase since the 1960s, with Mars playing a significant role in our quest for further knowledge. As the ambition to colonize Mars becomes a reality through the collaboration of private companies and space agencies, the need for reliable and robust communication infrastructures in the Martian environment becomes paramount. In this context, reconfigurable intelligent surface (RIS)-empowered communication emerges as a promising technology to enhance the coverage due to lack of multipath components in line-of-sight (LOS) dominated Martian environments. By considering various Martian scenarios such as canyons, craters, mountains, and plateaus, this article explores of the potential of RISs in increasing the coverage in Martian environments. The article also provides an overview of RIS-assisted localization in both LOS and non-line-of-sight (NLOS) scenarios, presenting a general framework for accurate user angle estimation in challenging Martian conditions. The findings and presented framework of this article provide a promising research direction for integrating RISs in deep space communication as well as paving the way for future improvements in interplanetary communication networks.

eess.SP↗

arXiv2025

A Practical Validation of RIS Detection and Identification

Reconfigurable intelligent surface (RIS)-assisted communication is a key enabling technology for next-generation wireless communication networks, allowing for the reshaping of wireless channels without requiring traditional radio frequency (RF) active components. While their passive nature makes RISs highly attractive, it also presents a challenge: RISs cannot actively identify themselves to user equipments (UEs). Recently, a new method has been proposed to detect and identify RISs by letting them modulate their identities in the signals reflected from their surfaces. In this letter, we first propose a new and simpler modulation method for RISs and then validate the concept of RIS detection and identification (RIS-ID) using a real-world experimental setup. The obtained results validate the RIS-ID concept and show the effectiveness of our proposed modulation method over different operating scenarios and systems settings.

eess.SP↗

arXiv2025

A Novel Partitioning Scheme for RIS Identification and Beamforming

This letter introduces a novel partitioning scheme for reconfigurable intelligent surfaces (RISs) that simultaneously consider RIS identification and beamforming. The proposed scheme dynamicly and efficiently allocates RIS elements between identification and beamforming users, considering the different performance metrics associated with each of them. By employing a dynamic partitioning algorithm that efficiently manage the RIS resources (elements), the scheme significantly enhances the signal-to-noise ratio (SNR) while maintaining reliable identification performance. Finally, theoretical analysis and computer simulations are provided to demonstrate the validity of the proposed scheme.

eess.SP↗

arXiv2025

A Simple Detection and Identification Scheme For Reconfigurable Intelligent Surfaces

Reconfigurable intelligent surface (RIS)-empowered communication is one of the promising physical layer enabling technologies for the sixth generation (6G) wireless networks due to their unprecedented capabilities in shaping the wireless communication environment. RISs are modeled as passive objects that can not transmit or receive wireless signals. While the passiveness of these surfaces is a key advantage in terms of power consumption and implementation complexity, it limits their capability to interact with the other active components in the network. Specifically, unlike conventional base stations (BSs), which actively identify themselves to user equipment (UEs) by periodically sending pilot signals, RISs need to be detected from the UE side. This paper proposes a novel RIS identification (RIS- ID) scheme, enabling UEs to detect and uniquely identify RISs in their surrounding environment. Furthermore, to assess the proposed RIS-ID scheme, we propose two performance metrics: the false and miss detection probabilities. These probabilities are analytically derived and verified through computer simulations, revealing the effectiveness of the proposed RIS-ID scheme under different operating scenarios.

eess.SP↗

arXiv2025

Clutter Suppression in Bistatic ISAC with Joint Angle and Doppler Estimation

The coexistence of radar and communications in wireless systems marks a paradigm shift for the sixth-generation (6G) networks. As 6G systems are expected to operate at higher frequencies and employ larger antenna arrays than fifth-generation (5G) systems, they can also enable more accurate sensing capabilities. To this end, the integrated sensing and communication (ISAC) paradigm aims to unify the physical and radio frequency (RF) domains by introducing the sensing functionality into the communication network. However, the clutter poses a challenge, as it can significantly degrade the sensing accuracy in ISAC systems. This paper presents a novel two-dimensional root multiple signal classification (2D-rootMUSIC)-based algorithm for static background clutter suppression. Computer simulation results indicate that the proposed method effectively mitigates the strong background clutter, yields accurate parameter estimation performance, and offers a notable improvement in the signal-to-clutter-and-noise ratio (SCNR), while outperforming the prior-art benchmark methods.

eess.SP↗

arXiv2025

A Survey of OTFS-Based Index Modulation Techniques: Challenges, Benefits, and Future Directions for 6G and Beyond

Orthogonal time frequency space (OTFS) is a two-dimensional modulation technique that uses the delay-Doppler (DD) domain and is a candidate for providing robust, high-capacity wireless communications for envisioned 6G and beyond networks. The OTFS technique maps data to the DD domain instead of the traditional time-frequency domain, enabling it to fully utilize channel diversity and transform fast time-varying channels into nearly static channels. Index modulation (IM) is a communication paradigm that conveys information not only through conventional modulation symbols but also by encoding data bits in the indices of the selected communication resources to improve error performance, spectral efficiency, and energy efficiency. In this survey, a comprehensive review of work on OTFS-based wireless communication systems is presented. In particular, the existing OTFS-IM schemes are reviewed and systematically categorized according to their system architectures, detection methods, and performance aspects such as capacity, peak-to-average power ratio, diversity, complexity, imperfect channel state information, spectral efficiency, and outage probability. Furthermore, the operating principles and system models of OTFS-IM variants-including OTFS-based space shift keying, OTFS-based spatial modulation, OTFS-based quadrature spatial modulation, OTFS-based media-based modulation, and OTFS-based code index modulation-are described, followed by a comparative performance analysis in terms of computational complexity, error performance, capacity, energy saving, spectral efficiency, and throughput. Finally, the challenges, benefits, and future directions for OTFS-IM systems are discussed, covering key aspects such as complexity, efficiency, latency, channel estimation, hardware constraints, synchronization, security, and potential integration with other advanced wireless communication techniques.

eess.SP↗

arXiv2025

Modern Base Station Architecture: Enabling Passive Beamforming with Beyond Diagonal RISs

Beamforming plays a crucial role in millimeter wave (mmWave) communication systems to mitigate the severe attenuation inherent to this spectrum. However, the use of large active antenna arrays in conventional architectures often results in high implementation costs and excessive power consumption, limiting their practicality. As an alternative, deploying large arrays at transceivers using passive devices, such as reconfigurable intelligent surfaces (RISs), offers a more cost-effective and energy-efficient solution. In this paper, we investigate a promising base station (BS) architecture that integrates a beyond diagonal RIS (BD-RIS) within the BS to enable passive beamforming. By utilizing Takagi's decomposition and leveraging the effective beamforming vector, the RIS profile can be designed to enable passive beamforming directed toward the target. Through the beamforming analysis, we reveal that BD-RIS provides robust beamforming performance across various system configurations, whereas the traditional diagonal RIS (D-RIS) exhibits instability with increasing RIS size and decreasing BS-RIS separation-two critical factors in optimizing RIS-assisted systems. Comprehensive computer simulation results across various aspects validate the superiority of the proposed BS-integrated BD-RIS over conventional D-RIS architectures, showcasing performance comparable to active analog beamforming antenna arrays.

eess.SP↗