Browsing by Author "Develi, Ibrahim"

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Citation - Scopus: 1
Aber Performance of Ofdm-Im Systems by Ris Design in the Presence of Iqi and Α-Μ Fading
(Elsevier - Division Reed Elsevier India Pvt Ltd, 2024) Karahan, Busra; Develi, Ibrahim; Canbilen, Ayse Elif; Alsalameh, Hussam
Index modulation (IM) techniques are among the competitive candidates for fifth-generation and beyond (5GB) systems, offering new ways of conveying information thanks to their advantages such as structure flexibility and hardware convenience. Meanwhile, research on orthogonal frequency division multiplexing (OFDM) performance improvements for next-generation wireless communication systems is still intensively ongoing. Accordingly, the IM system has been adapted to OFDM, which allows additional bits of information to be transmitted through the subcarrier indices of the OFDM. Nevertheless, hardware impairments (HWIs) limit the performance of the transceiver. In the literature, reconfigurable intelligent surface (RIS) technology controls the propagation environment and enhances the quality of the received signal by modifying the phase of the incoming signal. In this paper, we investigate the effects of in-phase (I) and quadrature-phase (Q) imbalance (IQI) on RIS-based OFDM-IM transceivers motivated by the benefits of the RISs. Firstly, we present an RIS-assisted OFDM-IM model subject to transmitter and receiver IQI effects. Next, the average bit error rate (ABER) performance of the RIS-assisted OFDM-IM is calculated by the provided mathematical expressions taking the effect of IQI into account. The simulation outputs show that the designed RIS-supported scheme achieves a performance improvement compared to the traditional OFDM-IM under the effect of IQI.
Citation - WoS: 11
Citation - Scopus: 14
Error Bounds for 3d Localization and Maximum Likelihood Estimation of Mm-Wave Miso Ofdm Systems in the Presence of Hardware Impairments
(Ieee-Inst Electrical Electronics Engineers Inc, 2022) Tubail, Deeb Assad; Ceniklioğlu, Buşra; Canbilen, Ayşe Elif; Develi, Ibrahim; Ikki, Salama
Millimeter-wave (mm-wave) multiple-input single-output (MISO) systems are expected to be extremely advantageous for the fifth generation (SG) cellular systems. In fact, these systems are considered key enablers of centimeter-level localization accuracy, even in the case of a single base station (BS). However, there are still fundamental issues that need to be addressed when applying mm-wave MISO systems to practical scenarios, namely the effects of hardware impairments (HWIs). In this study, the 3D localization accuracy of mm-wave MISO OFDM systems is investigated when there are HWIs at both the BS and the mobile station (MS). The localization is performed by estimating the downlink channel parameters of the line-of-sight (LOS) path using only a maximum likelihood (ML) estimator at the MS. We then transform these channel parameters into ones for localization. The Fisher information matrix (FIM) is employed to assess the accuracy of the estimation processes, considering also any non-LOS (NLOS) paths. The limit of localization is calculated in terms of the position error bound (PEB). Computer simulations demonstrate the destructive impacts of HWIs on the localization process. Moreover, it was proven that the effect of NLOS paths from unknown scatters on the localization process is related to the ratio between LOS and NLOS path gains.
Error Performance of Df Cooperative Smts With I/Q Imbalance Over Beckmann Fading Channels
(ACADEMIC PRESS INC ELSEVIER SCIENCE, 2025) Canbilen, Ayşe Elif; Develi, Ibrahim; Gültekin, Seyfettin Sinan
The direct down-conversion principle, which has generally been used in the design of multiple-input multiple- output (MIMO) schemes, including space modulation techniques (SMTs), is attractive to researchers because of its low cost, low power consumption with fewer components, flexible and simple structure. However, hardware imperfections such as in-phase (I) and quadrature-phase (Q) imbalance (IQI) negatively affect the performance of the systems with direct down-conversion in practice. On the other hand, cooperative communication is a promising technology that can be utilized in the design of future wireless networks due to its significant advantages such as increasing system reliability, extending network coverage, reducing channel degradation, and providing high quality of service. In this study, SMT-based methods are integrated into cooperative systems, and a flexible and comprehensive model is presented that is applicable to many channel structures. Specifically, the error performance analysis of space shift keying (SSK), spatial modulation (SM), and quadrature SM (QSM) systems in the presence of IQI in decode-and-forward (DF) cooperative communication is carried out by analytical derivations and computer simulations over generalized Beckmann fading channels. The obtained results show that the performance of SMT-based DF cooperative systems is superior to the conventional schemes, and the effects of receiver IQI can be eliminated by optimal detector designs.
Performance Analysis of RIS-Empowered OFDM-IM Communications under Weibull Fading and Joint Tx/Rx I/Q Imbalance
(TÜBİTAK Scientific & Technological Research Council Turkey, 2025) Ceniklioglu, Busra; Develi, Ibrahim; Canbilen, Ayse Elif
A modernist technique, reconfigurable intelligent surface (RIS) provides outstanding signal reflection and amplification, making it highly valuable for upcoming communication systems. Besides, a major contributor is index modulation (IM), attaining superior spectral and energy efficiency, and achieving hardware sufficiency. The primary and novel contribution of this work is the derivation of a highly accurate, closed-form approximate expression for the average bit error rate (ABER) of an orthogonal frequency division multiplexing (OFDM)-IM system operating in the complex and challenging environment characterized by joint transmitter/receiver (Tx / Rx ) in-phase and quadraturephase imbalance (IQI) and Weibull fading. This essential analytical achievement is facilitated by the newly formulated, closed-form pairwise error probability (PEP) expression specifically tailored to the maximum likelihood (ML) detector used in this non-ideal, effect of IQI on OFDM-IM system over the fading channel. Furthermore, this analysis is uniquely applied to quantify the precise performance impact of various RIS configurations under these simultaneous impairments. In addition the RIS configuration is shown to significantly enhance the overall system performance. Our results reveal that integrating RIS with OFDM-IM systems is an effective strategy to alleviate the undesirable impact of joint Tx and Rx IQI. The final and conclusive step of the work solidifies the analytical novelty by demonstrating that the derived closed-form ABER expressions are robust and accurate, as evidenced by the perfect match between the theoretical (analytical) results and the detailed Monte Carlo simulation results.