Akademik Veri Yönetim Sistemi
Tezin Türü: Doktora
Tezin Yürütüldüğü Kurum: İstanbul Medipol Üniversitesi, Fen Bilimleri Enstitüsü, Türkiye
Tezin Onay Tarihi: 2024
Tezin Dili: İngilizce
Öğrenci: SALAH EDDINE ZEGRAR
Danışman: Hüseyin Arslan
Özet:
A 6G promises to have a variety of applications, as well as network entities, in terms of power, range, data rates, latency, and propagation environment. The overall heterogeneity of the network poses significant challenges in terms of physical (PHY) layer design. This thesis first identifies some of the areas where the 5G multi-numerology orthogonal frequency division multiplexing (OFDM) falls short before discussing the possible approaches towards PHY design. In particular, it is discussed that a backward-compatible, forward- looking, and extendable PHY layer framework can be extended as new requirements arise to enable a graceful and sustainable network evolution. Additionally, several candidate waveforms for 6G, such as Orthogonal Frequency Division Multiplexing (OFDM), Common-Cyclic Prefix (CCP) OFDM, orthogonal time-frequency-space (OTFS), frequency modulated continuous wave (FMCW), and orthogonal chirp division multiplexing (OCDM) are presented and investigated. Continuing with the use cases of these waveforms, first, the thesis proposes novel physical layer security (PLS) schemes for MIMO systems based on orthogonal frequency division multiplexing (OFDM). These schemes utilize minimum-phase all-pass channel decomposition to ensure security without compromising the performance of legitimate users. Furthermore, a novel transceiver design for CCP-OFDM is introduced, enabling low-complexity frequency-domain channel estimation and equalization. This design mitigates the need for complex time-domain estimation algorithms. The thesis explores a modified structure of the full-CP (FCP) in orthogonal time-frequency-space (OTFS) modulation, leveraging the FCP structure in the delay-Doppler domain to enhance system performance. Then, an impulse-based channel estimation method is proposed, utilizing the pulse-tone nature of the pilot impulse to estimate fractional delay and fractional Doppler channel with low complexity. In the context of integrated sensing and communication (ISAC), an OTFS-based system is proposed, enabling precise range-velocity profiles without the need for large bandwidth transmissions or long-duration frames. This approach relaxes constraints on bandwidth and time while providing accurate sensing information. To address the challenges associated with ISAC, a novel OTFS-FMCW waveform is proposed in this thesis. The waveform leverages the sparsity of linear chirps in the delay-Doppler domain to enable orthogonal multiplexing of OTFS and FMCW, facilitating simultaneous high data rate communication and low-complexity accurate sensing. Additionally, a multi- user ISAC scheme is presented, where multiple orthogonal chirps (OCs) are allocated to different users within the same OTFS-FMCW waveform. Finally, OCDM is explored as a potential 6G waveform. The thesis investigates the representation of OCDM waveforms in the delay-Doppler domain, revealing their sparse nature. Leveraging this observation, a low-complexity channel estimation technique is proposed, involving the design of pilots in the Fresnel domain and channel estimation in the delay-Doppler domain.