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Öğe A framework for Gaussian Q approximation with BSA and its application to RIS-assisted systems(Elsevier Gmbh, 2024) Bilim, Mehmet; Kabalci, YasinThis paper proposes a novel and improved Chiani approximation for the Gaussian Q-function by employing the backtracking search optimization algorithm (BSA). The proposed approximation includes only exponential terms which are comfortable for the mathematical functionality. Then, a wireless communication application of reconfigurable intelligent surface (RIS) structures, which are anticipated to play a crucial role in integrated sensing and communication (ISAC), has been presented. In the considered wireless communication scenario, the link between the source and RIS node is Nakagami-m fading, while the link between RIS node and the destination is Rayleigh fading. The received probability density function (PDF) expression of instantaneous signal to noise ratio for this system has been derived analytically. Using this derived PDF, the error expression (Pe) for the RISassisted communication system employing the rectangular quadrature amplitude modulation (RQAM) technique has been obtained with the assistance of the proposed improved Chiani approximation in this study. The obtained RQAM error figures are presented comparatively, and the results clearly show that the Pe expression by obtained the proposed approximation with BSA for the RIS-assisted communication system, which is an important aspect for ISAC, is in excellent agreement with computer simulations.Öğe Approximate Error Probability Analysis of L-Branch MRC System over ?-? Fading Environments(IEEE, 2024) Mutlu, Ural; Bilim, Mehmet; Kabalci, YasinThe increase in research conducted on next-generation communication systems has directed research interest toward new modulation schemes, channel models, and diversity techniques that promise enhanced efficiency. Recently, new analytical channel models capable of better modeling the wireless communication environment have been developed. In this study, the approximate error performance of hexagonal quadrature amplitude modulation (HQAM) in lambda - mu fading channels for multi-branch single-input multiple-output (SIMO) systems is investigated. An analytical expression for the error probability of the considered system is derived using the Prony approximation for the Gaussian Q function. Subsequently, an error probability expression for the considered system is proposed. Comparative results between the approximate results obtained from the derived expression and the exact simulation results are presented. Different scenarios are evaluated to analyze the effects of channel fading parameters, the number of transmission branches, and modulation levels, resulting in numerical outcomes. Ultimately, it was observed that the approximate results obtained from the proposed expression closely matched the exact simulation results, confirming the accuracy of the proposed analytical expression.Öğe Beaulieu-Xie Gölgelemeli Sönümlü Kanallar İçin Efektif Kanal Kapasite İfadesinin Kuramsal Türetimi(2022) Bilim, Mehmet; Kabalcı, YasinBu çalışma, alıcı-verici arasındaki hattın tek ve Beaulieu-Xie gölgelemeli (BX-shadowed, BX-S) sönümlenmeye sahip olduğu bir sistem için efektif kanal kapasitesi (effective channel capacity, Ceff) analizini sunmaktadır. Çalışmada Ceff ifadesi kuramsal olarak türetilmekte, türetimler için BX-S sönümlenmesine ait olasılık yoğunluk fonksiyonundan (probability density function, PDF) yararlanılmaktadır. Ceff ifadesinin doğruluğu bilgisayar benzetimleri ile gösterilmeye çalışılmakta, farklı parametre değişimleri ile çeşitli senaryolar incelenmektedir.Öğe Joint Channel Estimation and Localization in RIS Assisted OFDM-MIMO System(IEEE, 2024) Mutlu, Ural; Bilim, Mehmet; Kabalci, YasinReconfigurable Intelligent Surfaces (RISs) are expected to become one of the enabling technologies in the development of the sixth generation (6G) smart radio environment, where services such as localization and sensing are going to be ubiquitous and an integral part of the system. However, achieving localization in a dense urban environment is a challenging task. Therefore, this study considers joint channel and localization estimation in a RIS-assisted orthogonal frequency division multiplexing multiple-input multiple-output (OFDM-MIMO) system operating in a dense urban environment, where only Non-Line-of-Sight (NLoS) multipath components are available. The channel estimation is based on the channels being sparse in the spatial and angular domains and having only a few Angles of Arrival (AoA) and Angles of Departure (AoD), thus the channel estimation becomes a sparse signal recovery problem that can be solved with compressive sensing algorithms. The study implements Simultaneous Orthogonal Matching Pursuit (SOMP) to obtain AoA and AoD. The time delay parameters are obtained by correlating OFDM subcarriers with a search matrix. A localization estimation algorithm based on linearization of the estimated geometric parameters is adopted. The results of the study show that for a channel consisting of 3 NLoS paths, location estimation in the range of decimeters is possible.Öğe Outage Probability Analysis of RIS-Assisted System over Weibull/Rayleigh Fading Channels(IEEE, 2024) Mutlu, Ural; Bilim, Mehmet; Kabalci, YasinIn upcoming communication systems, particularly beyond fifth-generation (B5G) and sixth-generation (6G), reconfigurable intelligent surfaces (RIS) are anticipated to offer significant advancements. This study analyzes the outage probability of an RIS-aided communication system under Weibull and Rayleigh fading conditions. The proposed system model assumes Weibull fading for the channel between the source and RIS, while Rayleigh fading is assumed for the channel between RIS and destination. Numerical simulations are conducted across various configurations to assess the impact of different fading parameters, reflective surface elements, signal-to-noise ratio (SNR), and instantaneous SNR threshold values. Comparative analysis between the results obtained from the derived expression and exact results is presented. Notably, the analytical and simulation results exhibit strong consistency, indicating the robustness of the proposed approach.Öğe Performance of Two-Hop Relay Assisted Decode-and-Forward Transmission under Mixed Fading Environments(KAUNAS UNIV TECHNOLOGY, 2015) Kapucu, Nuri; Bilim, Mehmet; Develi, Ibrahim; Kabalci, YasinThis study analyses the performance of two-hop decode-and-forward (DF) relaying protocol under mixed faded channels by evaluating outage probability (P-out) and average bit-error probability (ABEP). It is assumed that the channel between source and relay is Rayleigh fading, whereas the relay-destination link is subject to Weibull fading. First, a closed-form expression is formulated for P-out and then it is used to obtain ABEP for the considered system model. The ABEP performance of two-hop DF relaying is presented for M-ary phase shift keying (M-PSK) signaling with different constellation sizes. Moreover, the proposed analytical expressions are verified by simulations that present the correctness of the derived formulas.Öğe POTENTIALLY TOXIC ELEMENTS OF VOLCANIC ASH SOILS IN THE CAPPADOCIA REGION OF CENTRAL TURKEY(NORTH UNIV BAIA MARE, 2015) Kilic, Kenan; Dogan, Hakan Mete; Yalcin, Huseyin; Bilim, Mehmet; Karahan, GulayWe determined the variability and content of potentially toxic elements (PTEs) in soils formed on volcanic parent materials erupted from Erciyes stratovolcano in the middle Anatolian region of Turkey. The PTE content of soils formed on tuffs were higher than the soils formed on lavas. All the PTE concentrations decrease with increasing soil depth except for those of Cd. Cr, Cd, and Ni increased with elevation, but Co, Cu, Mn, Pb, and Zn concentrations decreased. The high PTE concentrations in soils could be attributed to the volcanic parent materials. The greatest PTE variations in soils were determined by lithological differences and could be attributed to the types of parent material and their compositions. Site specific soil management practices must be applied to soils in the study area because of the high PTE content.Öğe Potentially toxic elements of volcanic ash soils in the Cappadocia region of central Turkey(North University of Baia Mare, 2015) Kiliç, Kenan; Doğan, Hakan Mete; Yalçin, Hüseyin; Bilim, Mehmet; Karahan, GülayWe determined the variability and content of potentially toxic elements (PTEs) in soils formed on volcanic parent materials erupted from Erciyes stratovolcano in the middle Anatolian region of Turkey. The PTE content of soils formed on tuffs were higher than the soils formed on lavas. All the PTE concentrations decrease with increasing soil depth except for those of Cd. Cr, Cd, and Ni increased with elevation, but Co, Cu, Mn, Pb, and Zn concentrations decreased. The high PTE concentrations in soils could be attributed to the volcanic parent materials. The greatest PTE variations in soils were determined by lithological differences and could be attributed to the types of parent material and their compositions. Site specific soil management practices must be applied to soils in the study area because of the high PTE content.Öğe The Next Generation in Communication Technology: Roadmap to 6G(IEEE, 2024) Cengiz, Alperen; Bilim, Mehmet; Kabalci, YasinSince the last quarter of 2022, studies on fifth-generation (5G) communication systems have been conducted under the name of beyond 5G studies. With the standardization of 5G communication systems, researchers have intensified their work on communication technologies beyond the 5G. The rapid advancements in communication technology have prompted 5G studies to focus on mapping out the roadmap for sixth-generation (6G) communication, which will be the next communication technology. This includes determining the vision and requirements for this new technology. This study investigates the developments in mobile communications from the first generation (1G) to the 5G, the main technologies and challenges in the fifth generation, and the expectations for 6G. It is expected that 6G will be operational by 2030 according to many researchers, countries, and companies.
