Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

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

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Author: search.filters.author.Altunbas, IbrahimLanguage: search.filters.language.en

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  • Conference Object
    Outage and Ser Analyses for Dual-Hop Inter-Satellite Thz Communication
    (IEEE, 2024) Ahrazoglu, Evla Safahan; Erdogan, Eylem; Altunbas, Ibrahim
    Inter-satellite links have crucial significance in offering global connectivity and low latency in satellite mega-constellations. In such architectures, system capacity and data-rate can be enhanced by utilizing terahertz (THz) frequencies. Considering the importance of inter-satellite links in mega-constellations and the mounting interest in THz communications, in this study, an inter-satellite THz communication system is examined. In this setup, a low earth orbit (LEO) satellite is deployed to assist transmission between two LEO satellites by using variable-gain amplify-and-forward relaying protocol. The system's performance is analyzed in terms of both outage probability and symbol error rate, and asymptotic outage characteristic is explored. All theoretical findings are verified by Monte-Carlo simulations.
  • 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.
  • Article
    Citation - WoS: 4
    Citation - Scopus: 3
    Design of Energy Efficient Multi-Haps Assisted Hybrid Rf/Fso Satellite Communication Systems With Optimal Placement
    (IEEE-Inst Electrical Electronics Engineers Inc, 2025) Ece Turk, Sare; Safahan Ahrazoglu, Evla; Erdogan, Eylem; Altunbas, Ibrahim
    Satellites and high altitude platform station (HAPS) systems are expected to become the key elements of non-terrestrial networks with the recent advances on sixth-generation (6G) wireless networks. In this article, motivated by the mounting interest in HAPS systems both from academia and industry, we propose a multi-HAPS aided optical satellite communication architecture using hybrid radio frequency (RF)/free space optical (FSO) communication to provide enhanced throughput, and reliability. The proposed architecture can be used in railways, transcontinental highways or maritime communications to provide enhanced coverage, throughput and reliability. To quantify the overall performance of the proposed scenario, outage probability, ergodic capacity, throughput, energy efficiency are obtained and validated. Additionally, the impact of outdated channel state information and channel estimation errors are considered, severely affecting the system performance by causing signal-to-noise ratio loss and outage floors. Furthermore, we find optimum HAPS distance and obtain the number of HAPS systems that is required for reliable communications. The results show that serial placement of HAPS systems at optimum distances can enhance the system performance and energy efficiency.