Yazar "Tusha, Seda" seçeneğine göre listele

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  • Küçük Resim
    Öğe
    Index modulation-based flexible waveform design
    (Institution of Engineering and Technology, 2020) Tusha, Seda; Tusha, Armed; Başar, Ertuğrul; Arslan, Hüseyin
    The service limitations of conventional orthogonal frequency division multiplexing (OFDM)-based technologies have motivated academia and industry to seek for new solutions in order to support the emerging services and use cases of future wireless networks. In this chapter, promising frequency-domain index modulation (IM) options, i.e., OFDM with IM (OFDM-IM), generalized OFDM with index modulation (OFDM-GIM), dual-mode OFDM (DM-OFDM), OFDM with interleaved subcarrier IM (OFDM-ISIM), are considered as complementary waveforms of classical OFDM. In frequency-domain IM, data information is sent not only via modulated subcarriers but also via proper activation of the subcarriers resulting in higher spectral efficiency (SE) and better error performance compared with OFDM-based schemes. Furthermore, features of OFDM, including intelligent subcarrier selection and adaptive activation ratio, are assessed. Lastly, the flexible utilization of these features is discussed to control channel effects, hardware impairments, asynchronicity, and to serve wide range requirements of fifth generation (5G) and beyond networks.
  • Küçük Resim Yok
    Öğe
    Interference and channel control techniques for the future of wireless communications
    (İstanbul Medipol Üniversitesi Fen Bilimleri Enstitüsü, 2020) Tusha, Seda; Arslan, Hüseyin
    Interference and random behavior of the propagation environment are the main impediments to serve a broad range of applications and use-cases in modern communication systems. Although conventional orthogonal multiple accessing (OMA) schemes are prominent for achieving high reliability, they are far from reaching the goals of 5G and beyond networks in terms of system capacity, massive connectivity, and latency. On the other hand, interest in high-frequency bands is growing due to the enormous amount of spare spectrum that has the potential to realize the aspirations of future communication systems. In addition to these considerations, next-generation communication systems require a flexible and scalable design to meet user equipment (UE) demands. For these reasons, this thesis study focuses on three pivotal research directions that control of interference in communication systems, control of channel randomness in millimeter wave (mmWave) bands, and the richness and flexibility of multidimensional signal transmission. In particular, non-orthogonal multiple accessing (NOMA) caused by partial and fully overlapping of the existing UEs, adaptive directional communication against low penetration capabilities in mmWave frequency band, and index modulation (IM)-aided multidimensional transmission for achieving flexibility are studied in the scope of this thesis. Despite all the efforts, having effective multiple access under non-orthogonal conditions is still a conundrum in the literature. As a promising approach, waveform domain NOMA concept is introduced for serving multiple users with different requirements. The goal of waveform domain NOMA is to control interference by means of unique waveform features and consequently ensuring the separability of the overlapped UEs at the receiver. Specifically, the control of interference distribution is provided via the coexistence of appropriate waveforms while the average power of the interference remains the same. Moreover, diversity gain is achieved through interference hopping during repetitions. Moreover, intercarrier-interference (ICI) control for asynchronous networks and inter-numerology interference (INI) control for OFDM systems with multi-numerologies are studied via the exploitation of frequency domain IM, i.e., OFDM-IM, with the design of novel subcarrier mapping schemes. Directional communication in mmWave bands provides opportunities to combat high-level propagation loss. However, initiating communication over a certain direction makes the link vulnerable against low penetration capabilities, i.e., blockage impact. Beamwidth optimization in mmWave frequency bands is proposed in order to combat high path loss and blockage impact. Lastly, IM-aided multidimensional communication opportunities are surveyed in a comprehensive manner. Specifically, a framework is developed for the purpose of efficient utilization of signal dimensions in order to address diverse requirements of 5G and beyond systems.
  • Küçük Resim
    Öğe
    Non-orthogonal radio access technologies
    (Institution of Engineering and Technology, 2020) Tusha, Armed; Tusha, Seda; Arslan, Hüseyin
    The radio resource scarcity of classical orthogonal radio access-based technologies has encouraged academia and industry to search for a way out in order to support the exponential growth of data rate, system capacity, and communication latency in beyond 5G wireless communications. Recently, the concept of nonorthogonal radio accessing, where user equipment (UEs) with different services intentionally share the same radio resources, is proposed to compensate the radio resource scarcity. The focus of this chapter is to emphasize the potential of nonorthogonal access technologies in next generation networks. The fundamentals of power-domain non-orthogonal multiple accessing (PD-NOMA) are revised considering system sum-rate and user fairness and compared with conventional orthogonal frequency division multiple access (OFDMA). Furthermore, state-of-the-art NOMAbased schemes, including low-density spreading (LDS) and index modulation (IM), grant-free (GF) random access, and relatively novel concept of waveform coexistence for multiple accessing, are discussed. Finally, future directions and potential non-orthogonal radio access technologies are analyzed considering practical scenarios.