arXiv subjects

Gokce Hacioglu

Publications and source records attributed to Gokce Hacioglu.

6 recordsLinked to original sources

arXiv2026

Periodic OFDMA: A Low-PAPR Multiple Access Scheme for Uplink Communications in 5G and Beyond

Multiple access techniques are vital for 5G and beyond. While Orthogonal Frequency Division Multiple Access (OFDMA) is standard, its high peak-to-average power ratio (PAPR) reduces energy efficiency in uplink transmissions. This paper presents Periodic OFDMA (P-OFDMA), a novel multiple access scheme with reduced PAPR and computational complexity. By assigning subcarriers in a periodic pattern across the entire frequency band, P-OFDMA enhances frequency diversity and simplifies allocation. We also introduce two precoded variants: P-OFDMA-DCT and P-OFDMA-DFT. Comprehensive simulations comparing P-OFDMA with OFDMA and SC-FDMA show that P-OFDMA-DFT consistently achieves the lowest PAPR. Furthermore, the standard P-OFDMA scheme outperforms SC-FDMA in PAPR for low subcarrier-per-user scenarios and achieves better bit error rate (BER) performance under high delay-spread conditions. Notably, P-OFDMA and its variants reduce transmitter-side processing by up to an eightfold factor compared to SC-FDMA, greatly benefiting low-complexity uplink devices. Although receiver complexity increases, the overall system processing load decreases, yielding improved energy efficiency. Thus, P-OFDMA offers a robust, energy-efficient uplink solution for future wireless networks.

eess.SP↗

arXiv2025

Filterless Multi-Color VLC via DC-Biased QCT

Multi-color visible light communication (VLC) can increase throughput and enable joint lighting and communication operation, but practical color-based schemes such as color shift keying (CSK) typically rely on receiver optical filters whose nonideal passbands and spectral overlap introduce color crosstalk and significant SNR loss. This paper proposes a DC-biased quartered composite transform (QCT) transmission framework for quadrichromatic red, amber, green, blue (RAGB) luminaires that enables filterless multiple streams reception with a single photodiode. The method partitions the information symbols into four parallel real-valued streams and applies a set of mutually orthogonal QCT synthesis matrices designed from the invariances of the matched-filtered circulant channel; at the receiver, matched filtering and QCT-domain projection yield four decoupled scalar subchannels that admit single-tap equalization. A unified evaluation is carried out under common illumination constraints (CCT/CRI and illuminance uniformity) and throughput-matched configurations against RAGB-CSK and conventional DCO-OFDM baselines. In an indoor scenario, QCT attains up to 48.95 dB average effective SNR, providing 15.1-22.7 dB gain over CSK and 15.6-26.4 dB gain over DCO-OFDM, while achieving essentially identical BER to DCO-OFDM in linear AWGN. Under matched mean optical power, QCT also yields near zero clipping distortion and a consistent 0.7-1 dB PAPR reduction relative to DCO-OFDM, supporting power efficient and robust filterless multi-color VLC without sacrificing lighting quality.

eess.SP↗

arXiv2024

NOMA-CSK Integrated VLC System with Reinforcement Learning-Based Multi-Objective Power Allocation

This paper introduces a novel framework that synergistically combines Non-Orthogonal Multiple Access (NOMA) with Color Shift Keying (CSK) modulation to substantially boost spectral efficiency in Visible Light Communication (VLC) systems. A key challenge in the proposed NOMA-CSK architecture is managing the complex power allocation process, especially under cross-color interference caused by spectral overlap among LEDs and the limitations of optical filters. To overcome this, we develop an intelligent power allocation strategy powered by a Soft Actor-Critic (SAC) reinforcement learning agent. Trained in a simulated indoor environment, the SAC agent dynamically distributes power among users with diverse channel conditions while balancing multiple performance objectives. Simulation results show that our SAC-based method significantly outperforms traditional approaches such as Gain Ratio Power Allocation (GRPA) and Normalized Gain Difference Power Allocation (NGDPA), achieving superior fairness, higher overall throughput, and reduced bit error rates - even under a challenging 10 dB SNR. Notably, the trained agent demonstrates strong generalization capabilities, maintaining optimal performance in unseen environments without requiring retraining. Overall, this work makes two major contributions: it presents a pioneering NOMA-CSK VLC system design and delivers a robust, adaptive power allocation solution critical for real-world applications.

eess.SP↗

arXiv2024

A Novel Approach to Fair Power Allocation for NOMA in Visible Light Communication

This paper addresses the growing demand for high-bandwidth wireless data transmission by exploring Visible Light Communication (VLC) as an alternative to Radio Frequency (RF) communication. In indoor scenarios, VLC systems utilize existing lighting infrastructure for high-speed data transmission. To meet the data rate demands of 5G and beyond, the paper proposes Non-Orthogonal Multiple Access (NOMA) and introduces Empirical Fair Optical Power Allocation (EFOPA) to simplify resource allocation in NOMA. EFOPA integrates NOMA with VLC, utilizing the Artificial Bee Colony (ABC) optimization algorithm for offline resource allocation planning. The approach then derives a simplified power allocation equation from ABC outcomes, ensuring fair resource distribution among users. EFOPA is compared against existing power allocation methods, demonstrating superior fairness and reduced computational complexity. Numerical evaluations reveal EFOPA consistently outperforms other methods across various channel conditions, making it a robust and efficient solution for fair power allocation in NOMA-VLC systems.

eess.SP↗

arXiv2023

A Novel Pre-Coding Based PAPR Reduction Scheme for IM/DD Systems

Orthogonal frequency division multiplexing (OFDM) is critical for high-speed visible light communication (VLC) transmission; however, it suffers from a high peak-to-average power ratio (PAPR) problem. Among PAPR reduction techniques, pre-coding methods have shown promising advantages such as signal independence and no requirement for signaling overhead. In this paper, we present a novel pre-coding method that combines discrete cosine transform (DCT) and discrete sine transform (DST) for VLC systems using OFDM. Our proposed approach, tailored specifically for intensity modulation and direct detection (IM/DD) systems, aims to further improve the PAPR reduction while preserving bit error rate (BER) performance. Simulation results demonstrate that the proposed method achieves more than a 6 dB reduction in PAPR compared to the DCT pre-coded method without significant degradation in BER performance.

eess.SP↗

arXiv2021

Optical OFDM Waveform Construction by Combining Real and Imaginary Parts of IDFT

In optical communication systems, orthogonal frequency division multiplexing (OFDM) is widely used to combat inter-symbol interference (ISI) caused by multipath propagation. Optical systems which use intensity modulation and direct detection (IM/DD) can only transmit real valued symbols, but the inverse discrete Fourier transform (IDFT) or its computationally efficient form inverse-fast Fourier transform (IFFT) required for the OFDM waveform construction produces complex values. Hermitian symmetry is often used to obtain real valued symbols. For this purpose, some trigonometric transformations such as discrete cosine transform (DCT) are also used, however these transformations can eliminate the ISI only under certain conditions. In this paper, we propose a completely different method for the construction of OFDM waveform with IFFT to obtain real valued symbols by combining the real and imaginary parts (CRIP) of IFFT output electrically (E-CRIP) or optically (O-CRIP). Analytical analysis and simulation works are presented to show that compared to the Hermitian symmetric system, the proposed method slightly increases the spectral efficiency, eliminates ISI, significantly reduces the amount of needed calculation and does not effect the error performance. In addition, the O-CRIP method is less affected by clipping noise that may occur due to the imperfections of the transmitter front-ends.

cs.IT↗