Yazar "Althunibat, Saud" seçeneğine göre listele

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    A secure downlink NOMA scheme against unknown internal eavesdroppers
    (IEEE-Institute of Electrical and Electronics Engineers Inc., 2021) Abushattal, Abdelrahman; Althunibat, Saud; Qaraqe, Marwa; Arslan, Hüseyin
    Enhancing security level against potential internal eavesdroppers in Non-Orthogonal Multiple Access (NOMA) has been reported as a serious challenge. In this letter, a novel secure NOMA scheme based on physical-layer security concepts is proposed. The proposed scheme exploits the random and independent channel characteristics to induce a different phase shift in each user's symbol. Based on the assumption that the instantaneous channel phase between a user and the base station is available only at both ends, other users will not be able to decode the right symbol. Analytical and simulation average bit error rate performance results demonstrate the ability of the proposed scheme to degrade the performance at the eavesdropper without affecting the performance at other legitimate users and guarantee data confidentiality of each user.
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    Exploiting user diversity in OTFS transmission for beyond 5G wireless systems
    (Institute of Electrical and Electronics Engineers Inc., 2022) Tusha, Armed; Althunibat, Saud; Hasna, Mazen O.; Qaraqe, Khalid; Arslan, Hüseyin
    Orthogonal time frequency space (OTFS) modulation is a recent technology that offers a significant advantage on link reliability due to its strong delay-Doppler resilience. In classical cellular technology, overall system performance is limited by the fading and interference experienced by particular user equipment (UE) over its radio resources (RR). Besides, OTFS performance depends on the channel diversity of the UEs. Therefore, this letter examines the potential of multi-user diversity for OTFS systems considering practical scenarios. Specifically, we introduce a novel scheduling algorithm that proposes the assignment of the available RR of OTFS frame to the UE with the largest number of channel taps, resulting in enhanced channel diversity. It is shown via both mathematical analysis and simulation results that the proposed scheduling technique outperforms the scheme with random access to delay-Doppler RR in terms of system bit error rate (BER) with maximum likelihood (ML) receiver. The BER results validate the accuracy of the proposed technique for OTFS transmission with minimum mean square error (MMSE) detector considering various system configurations.
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    Index modulation-aided IQ imbalance compensator for OTFS communications systems
    (Institute of Electrical and Electronics Engineers Inc., 2022) Tusha, Armed; Dogan Tusha, Seda; Althunibat, Saud; Başar, Ertuğrul; Qaraqe, Khalid; Arslan, Hüseyin
    Design of simple transceiver architectures is inevitable in order to provide low computational complexity, low power consumption and affordable cost in beyond 5G (B5G) wireless systems, but it results in hardware impairments that significantly degrade the performance reliability of transmission. In this paper, among these hardware impairments, we discuss in-phase and quadrature (IQ) imbalance in orthogonal time frequency space (OTFS), which is a recent waveform considered as a potential candidate for B5G systems to relax the vulnerability against time-variant wireless channels. To mitigate the effect of IQ imbalance for OTFS, we propose an energy and spectral efficient IQ imbalance compensation scheme with the aid of index modulation (IM), which provides an attractive flexibility in the system design. In contrast to conventional solutions used in classical wireless technologies, such as iterative and pilot-based techniques, the proposed scheme avoids additional energy consumption and significant spectral efficient loss during the estimation and compensation of the IQ imbalance effect. The obtained bit error rate (BER) results validate the accuracy of the proposed compensator for different OTFS system configurations considering perfect/imperfect channel state information in practical scenarios.
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    Inter-numerology interference in OFDM-IM systems
    (Wiley, 2021) Doğan Tusha, Seda; Tusha, Armed; Başar, Ertuğrul; Althunibat, Saud; Qaraqe, Khalid; Arslan, Hüseyin
    In 5G and beyond communication systems, distinct numerologies can coexist to serve diverse requirements for users and applications. However, the inter-numerology interference (INI) is a main challenge that significantly impacts the system performance. Therefore, the performance under INI has become an essential evaluation metric for the suitability of the different transmission schemes in the future communication systems. This paper analyzes the impact of INI on the performance of orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems. Specifically, an analytical expression of the INI level in OFDM-IM systems is presented as a function of the subcarrier activation ratio (SAR) and subcarrier activation probability (SAP). Furthermore, aiming at reducing the INI level, an adaptive subcarrier mapping scheme (SMS) is proposed based on the conventional combinatorial mapping scheme. Moreover, analysis and evaluation of SAR and SAP are performed regarding the requirements of 5G and beyond services. It is proved that the INI level in OFDM-IM systems is highly dependent not only on the number of active subcarriers but also on their position in an OFDM block.
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    On the inherent physical-layer security of receive spatial modulation systems
    (Institute of Electrical and Electronics Engineers Inc., 2020) Abushattal, Abdelrahman; Althunibat, Saud; Qaraqe, Marwa; Arslan, Hüseyin
    This paper investigates the physical-layer security attained by Receive Spatial Modulation (RSM) scheme against potential eavesdroppers. The impact of the involved parameters on the bit error rate (BER) at the legitimate receiver and the considered eavesdropper is shown and discussed. Moreover, a hybrid scheme is proposed in order to alleviate the impact of the channel estimation errors on the achievable BER at the legitimate receiver. The proposed scheme allows the transmitter to switch between RSM and the conventional SM based on the phase of the estimated channel coefficient. Simulation results reveal that the proposed scheme can achieve at least 3 dB SNR gain as compared to the RSM, while keeping the error rate at the eavesdropper within acceptable bound.
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    Orthogonal time frequency space multiple access using index modulation
    (Institute of Electrical and Electronics Engineers Inc., 2023) Doğan Tusha, Seda; Tusha, Armed; Althunibat, Saud; Qaraqe, Khalid
    Orthogonal time frequency space (OTFS) is a recent two-dimensional modulation technique utilizing delay-Doppler domain and nominated as a promising candidate waveform for beyond 5G communication systems. By leveraging both time and frequency selectivity of doubly-dispersive radio channels, it has shown a better performance compared to traditional schemes. OTFS offers different options for accommodating multiple users on a given resource block. This article introduces a novel OTFS based uplink multiple access scheme by means of index modulation (IM) in delay-Doppler domain. IM based OTFS multiple access (OTFS-IMMA) proposes the coexistence of multiple users over the same delay-Doppler resources. Unlike conventional OTFS multiple access schemes, OTFS-IMMA allows users to employ IM to activate a subset of the available delay-Doppler resources without a coordination by the base station. Although data collision may occur between the users, our analysis shows that the achievable performance is still better than other schemes. Moreover, the proposed OTFS-IMMA scheme paves the way for flexible resource utilization in OTFS-MA to satisfy various users' demands in beyond 5G systems. It has been shown via both mathematical analysis and simulations that the proposed OTFS-IMMA scheme offers significant enhancement not only on bit error rate performance but also on the overall system efficiency. In addition, the achieved performance gain through OTFS-IMMA further increases as the number of channel taps and/or the number of delay-Doppler bins increase.
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    Performance analysis of OTFS under in-phase and quadrature imbalance at transmitter
    (IEEE-Institute of Electrical and Electronics Engineers Inc., 2021) Tusha, Armed; Doğan Tusha, Seda; Yılmaz, Ferkan; Althunibat, Saud; Qaraqe, Khalid; Arslan, Hüseyin
    The influence of in-phase and quadrature (IQ) imbalance on the performance of orthogonal time frequency space (OTFS) transmission is investigated in this work. OTFS is a recent two-dimensional transmission scheme with promising robustness against the time and frequency selectivity of the time-varying wireless channel, and IQ impairment arises from inevitable imperfections between in-phase and quadrature branches in the transceiver design. In this paper, the mathematical model is presented to illustrate the physical effect of the IQ mismatched transmitter in OTFS, which results in a new type of interference named mirror-Doppler interference (MDI), occurring only along the Doppler axis. Moreover, a closed-form expression for the average bit error rate (BER) of OTFS with IQ imbalanced transmitter is derived taking into account M-ary symbol with a constant envelope and maximum likelihood (ML) detection principle. Importantly, our findings prove that IQ imbalanced transmitter causes a significant reduction in the diversity gain of OTFS transmission, but does not lead to an error floor in the BER performance as in one-dimensional current communication systems. Monte-Carlo simulations are provided to validate the derived mathematical formulas for OTFS transmission with constant envelope M-ary symbols under different system configurations.
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    Physical effect of in-phase and quadrature imbalance in delay-doppler domain
    (Institute of Electrical and Electronics Engineers Inc., 2021) Tusha, Armed; Doğan Tusha, Seda; Yılmaz, Ferkan; Althunibat, Saud; Qaraqe, Khalid; Arslan, Hüseyin
    Orthogonal time frequency space (OTFS) technique is a recent two-dimensional (2-D) modulation aiming to exploit both time and frequency selectivity of doubly dispersive wireless channel, which significantly affects the reliability of conventional wireless communication systems. In OTFS transmission, delay-Doppler domain is utilized for conveying the data symbols. Besides channel characteristics, the performance of wireless communications systems is severely limited due to the impairments at the RF front-end. One of these impairments is the in-phase and quadrature (IQ) imbalance that occurs due to inevitable imperfections existing between in-phase and quadrature branches at either transmitter (Tx) or receiver (Rx) architecture. The aim of this paper is to reveal and investigate the physical effect of IQ impairment in delay-Doppler domain, which is unknown in the literature. Hence, we provide theoretical models to explicitly understand the impact of IQ imbalance at different stages of OTFS-based communication systems including Tx, Rx, and jointly Tx-Rx. Importantly, we show that although the performance of OTFS transmission depends on both delay and Doppler axes, IQ imbalance leads to an interference originating only from the mirror Doppler axes, which we name mirror Doppler interference (MDI), along with power degradation. Moreover, we assess the performance of IQ imbalanced OTFS under various communication scenarios considering ideal and practical pulse shapes with maximum likelihood (ML) and minimum mean square error (MMSE) detectors, respectively.