Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

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Access type: Open accessAuthor: search.filters.author.Altunbas, Ibrahim

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  • Conference Object
    Outage and Intercept Performance in THz LEO-Ground Communication With Satellite Selection
    (IEEE, 2025) Bakirci, Emre Berker; Ahrazoglu, Evla Safahan; Altunbas, Ibrahim; Erdogan, Eylem
    Satellite communication and THz communication systems are some of the methods that aim to meet the demand of increasing data rates. With an importance growing alongside increasing data amounts, data security is on its way to a position that cannot be neglected when building systems. In this study, it has been shown that secure data transmission can be made possible through the use of THz frequencies in a link between LEO satellites and a ground station. Proposed scenarios data transmission performance have been analyzed. It has been shown that selection transmission have improved both data transmission and security performances.
  • Article
    Citation - WoS: 1
    Citation - Scopus: 1
    An Improved Pointing Error Model for Mmwave and Thz Links: Antenna and Array Design Impact
    (IEEE-Inst Electrical Electronics Engineers inc, 2025) Ahrazoglu, Evla Safahan; Gul, Ahmet Caner; Akinci, Mehmet Nuri; Altunbas, Ibrahim; Erdogan, Eylem
    Pointing error has a significant impact on the performance of millimeter wave (mmWave) and terahertz (THz) communications due to directional transmission. Currently existing pointing error models are lacking in capturing the mmWave/THz radiation characteristics and/or the impact of antenna design and array design. Therefore, in this letter, a simple analytical pointing error model for highly directional mmWave/THz transmission is proposed. By utilizing the Gaussian beam approximation for both the array element radiation pattern and the array factor, the presented model incorporates antenna design parameters (maximum gain and 3 dB beamwidth) and array design parameters (number of array elements, element spacing, and 3 dB beamwidth). This approximation is validated via electromagnetic simulations in CST Microwave Studio. Afterwards, the statistics of the pointing error are derived according to the Gaussian beam approximation, and it is demonstrated that the pointing error follows a special case of the negative log-Gamma distribution with the shape parameter of 2 and the scale parameter depending on antenna/array design and jitter variance. It is shown that the proposed model aligns perfectly with the simulation results. Moreover, the outage performance of an aerial communication scenario is analyzed to examine the impact of pointing errors. The results have revealed that the antenna and array design parameters are as influential as the jitter variance, and they cannot be neglected.
  • Article
    Secrecy performance of full-duplex space-air integrated networks in the presence of active/passive eavesdropper, and friendly jammer
    (Wiley, 2024) Buyuksar, Ayse Betul; Erdoğan, Eylem; Altunbas, Ibrahim
    In this paper, a full-duplex (FD) space-air ground integrated network (SAGIN) system with passive and active eavesdroppers (PE/AE) and a friendly jammer (FJ) is investigated. The shadowing side information (SSI)-based unmanned aerial vehicle relay node (URN) selection strategy is considered to improve signal-to-interference plus noise power ratio (SINR) at the ground destination unit. To quantify the secrecy performance of the considered scenario, outage probability (OP), interception probability (IP), and transmission secrecy outage probability (TSOP) are investigated in the presence of FJ and PE/AE. The results have shown that aerial AE is an important threat since it can severely degrade the OP of the main transmission link. Furthermore, the FJ can decrease the IP of the eavesdropper by causing interference with the cost of power consumption of URNs. Simulations are performed to verify the theoretical findings.
  • Article
    Citation - WoS: 1
    Citation - Scopus: 1
    Multi-Haps Thz Satellite Communication: Error and Capacity Analyses Under I/Q Imbalance
    (Ieee-inst Electrical Electronics Engineers inc, 2024) Ahrazoglu, Evla Safahan; Altunbas, Ibrahim; Erdogan, Eylem
    Satellite communication (SatCom) has become an important field of research to accomplish the requirements of next-generation wireless communication systems such as high data rates and capacity while providing global coverage. Besides traditional communication applications, SatCom is gathering more and more attention as it enhances the performance of sensing applications, such as environmental monitoring, atmospheric pollution monitoring, and so on. To deliver worldwide service and improve accurate data collection in sensor networks, high-altitude platform station (HAPS) systems can be employed in SatCom. Moreover, utilizing terahertz (THz) frequencies in HAPS-assisted SatCom systems offers incredibly high bandwidths, enabling extreme data rates and higher resolution in sensing applications. In this article, a THz SatCom system model is considered where K number of HAPS systems are deployed to assist the transmission between a low-Earth-orbit satellite and a ground station by utilizing variable-gain amplify-and-forward (AF) relaying. The symbol error rate (SER) and ergodic capacity analyses are performed in the presence of attenuation depending on the atmospheric conditions, fading, pointing error (PE), and in-phase and quadrature (I/Q) imbalance. Theoretical findings are validated through Monte-Carlo simulations.
  • Conference Object
    Citation - Scopus: 2
    Outage Probability Analysis of Triple-Hybrid Rf/Fso Communication System
    (Ieee, 2024) Bakirci, Emre Berker; Ahrazoglu, Evla Safahan; Altunbas, Ibrahim; Erdogan, Eylem
    Terahertz (THz) and free space optical (FSO) transmission techniques are considered as alternatives for radio frequency (RF) transmission to meet the requirements for the sixth generation and beyond wireless communication systems. However, these transmission techniques may experience high level of deterioration under different weather conditions. In this study, triple-hybrid RF/FSO/THz system is proposed to enhance the system performance. The results have shown that the proposed system has improved outage probability performance under wide range weather conditions compared to only RF, only FSO, and only THz systems as well as dual-hybrid systems (RF/FSO, RF/THz, and FSO/THz). Theoretical results are validated via computer simulations.