109 citations · 144 across the 34 of their papers we have counts for
38 papers
Spectral Efficiency Analysis of Massive MIMO-OFDM Systems with Double Quantization
Bengu Bilgic Keskin, A. Oguz Kislal, Ali Gorcin +1
Massive multiple-input multiple-output (MIMO) achieves a high spectral efficiency (SE) by employing a large number of receive antennas in the uplink. Employing many receive antenna…
Fundamentals of Energy-Efficient Hardware Configurations for Wireless Links with Sleep Modes
Anders Enqvist, Özlem Tuğfe Demir, Cicek Cavdar +1
In this paper, we examine the energy efficiency (EE) of a base station (BS) with multiple antennas. We use a state-of-the-art power consumption (PC) model that captures the passive…
Fronthaul-Efficient Cell-Free Massive MIMO via Stream-Adaptive Resolution Control
Özlem Tuğfe Demir, Sinan Gezici
We consider the uplink of a fronthaul-constrained cell-free massive MIMO system with a single multi-antenna user equipment (UE) transmitting multiple spatial streams to distributed…
Joint Quantized Precoding and Bit Allocation for Fronthaul-Constrained Cell-Free Massive MIMO
Özlem Tuğfe Demir
We study quantization-aware precoding for the downlink of cell-free massive MIMO systems with limited-resolution fronthaul. In such systems, the centrally designed precoder must be…
Uplink Hardware Impairments in OFDM-Based Cell-Free Massive MIMO With Impaired Wireless Fronthaul
Özlem Tuğfe Demir
This paper studies the uplink performance of OFDM-based cell-free massive MIMO systems in the presence of hardware impairments affecting both low-cost access points and wireless fr…
Dual-polarized RIS versus dual-polarized network-controlled repeater
Özlem Tuğfe Demir
We study the achievable rate performance of dual-polarized passive reconfigurable intelligent surfaces (RISs) and dual-polarized network-controlled repeaters (NCRs) in a point-to-p…
Energy-Efficient Integrated Access and Fronthaul for Cell-Free Massive MIMO with Adaptive Quantization Resolution
Özlem Tuğfe Demir
Cell-free massive MIMO with wireless fronthaul is a promising architecture for energy-efficient 6G networks, but the access and fronthaul links must then share the same scarce spec…
Performance Analysis for ISAC Systems with 1-bit DACs
Murat Babek Salman, Özlem Tugfe Demir, Emil Björnson
Low-resolution quantization constrains the maximum achievable gains of multiple-input multiple-output (MIMO) systems. While the adverse effects and mitigation strategies have been…
RIS-Assisted Survivable Backhaul Recovery in Small-Cell Systems
Zhenyu Li, Özlem Tuğfe Demir, Emil Björnson +1
The increasing densification of small-cell networks substantially expands cable-based backhaul infrastructure, creating heightened vulnerability to cable link failures. This paper…
Learning Energy-Efficient Modular Arrays under Hardware Non-linearities
Özlem Tuğfe Demir, Alva Kosasih
This paper investigates the joint optimization of power allocation and antenna activation in sparse extremely large aperture array systems operating under power amplifier non-linea…
Stream-Adaptive Quantization and Power Allocation in Fronthaul-Constrained MIMO Systems
Özlem Tuğfe Demir, Emil Björnson
Many wireless systems divide the baseband processing between two locations, interconnected by a fronthaul. This paper examines the impact of fronthaul quantization on multiple-inpu…
Near-Field Beamfocusing, Localization, and Channel Estimation with Modular Linear Arrays
Alva Kosasih, Özlem Tuğfe Demir, Emil Björnson
This paper investigates how near-field beamfocusing can be achieved using a modular linear array (MLA), composed of multiple widely spaced uniform linear arrays (ULAs). The MLA arc…
Efficient Channel Estimation With Shorter Pilots in RIS-Aided Communications: Using Array Geometries and Interference Statistics
Özlem Tuğfe Demir, Emil Björnson, Luca Sanguinetti
Accurate estimation of the cascaded channel from a user equipment (UE) to a base station (BS) via each reconfigurable intelligent surface (RIS) element is critical to realizing the…
Near-Field Signal Processing: Unleashing the Power of Proximity
Ahmet M. Elbir, Özlem Tuğfe Demir, Kumar Vijay Mishra +2
After nearly a century of specialized applications in optics, remote sensing, and acoustics, the near-field (NF) electromagnetic propagation zone is experiencing a resurgence in re…
Spatial Frequencies and Degrees of Freedom: Their Roles in Near-Field Communications
Alva Kosasih, Özlem Tuğfe Demir, Nikolaos Kolomvakis +1
As wireless technology begins to utilize physically larger arrays and/or higher frequencies, the transmitter and receiver will reside in each other's radiative near field. This fac…
Spatial Correlation Modeling and RS-LS Estimation of Near-Field Channels with Uniform Planar Arrays
Özlem Tuğfe Demir, Alva Kosasih, Emil Björnson
Extremely large aperture arrays (ELAAs) can offer massive spatial multiplexing gains in the radiative near-field region in beyond 5G systems. While near-field channel modeling for…
Energy Reduction in Cell-Free Massive MIMO through Fine-Grained Resource Management
Özlem Tuğfe Demir, Lianet Méndez-Monsanto, Nicola Bastianello +2
The physical layer foundations of cell-free massive MIMO (CF-mMIMO) have been well-established. As a next step, researchers are investigating practical and energy-efficient network…
Destructive and constructive RIS beamforming in an ISAC-multi-user MIMO network
Steven Rivetti, Ozlem Tugfe Demir, Emil Bjornson +1
Integrated sensing and communication (ISAC) has already established itself as a promising solution to the spectrum scarcity problem, even more so when paired with a reconfigurable…
Wideband Channel Capacity Maximization With Beyond Diagonal RIS Reflection Matrices
Özlem Tuğfe Demir, Emil Björnson
Following the promising beamforming gains offered by reconfigurable intelligent surfaces (RISs), a new hardware architecture, known as \emph{beyond diagonal RIS (BD-RIS)}, has rece…
Malicious Reconfigurable Intelligent Surfaces: How Impactful can Destructive Beamforming be?
Steven Rivetti, Ozlem Tugfe Demir, Emil Bjornson +1
Reconfigurable intelligent surfaces (RISs) have demonstrated significant potential for enhancing communication system performance if properly configured. However, a RIS might also…
Multi-agent Reinforcement Learning for Energy Saving in Multi-Cell Massive MIMO Systems
Tianzhang Cai, Qichen Wang, Shuai Zhang +2
We develop a multi-agent reinforcement learning (MARL) algorithm to minimize the total energy consumption of multiple massive MIMO (multiple-input multiple-output) base stations (B…
Pilot Length Optimization with RS-LS Channel Estimation for Extremely Large Aperture Arrays
Mert Alıcıoğlu, Özlem Tuğfe Demir, Emil Björnson
Extremely large aperture arrays can enable unprecedented spatial multiplexing in beyond 5G systems due to their extremely narrow beamfocusing capabilities. However, acquiring the s…
Mixed Static and Reconfigurable Metasurface Deployment in Indoor Dense Spaces: How Much Reconfigurability is Needed?
Zhenyu Li, Ozan Alp Topal, Özlem Tuğfe Demir +2
In this paper, we investigate how metasurfaces can be deployed to deliver high data rates in a millimeter-wave (mmWave) indoor dense space with many blocking objects. These surface…
Parametric Near-Field Channel Estimation for Extremely Large Aperture Arrays
Alva Kosasih, Özlem Tuğfe Demir, Emil Björnson
Accurate channel estimation is critical to fully exploit the beamforming gains when communicating with extremely large aperture arrays. The propagation distances between the user a…