LEE- Telekomünikasyon Mühendisliği Lisansüstü Programı
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Gözat
Yazar "Başar, Ertuğrul" ile LEE- Telekomünikasyon Mühendisliği Lisansüstü Programı'a göz atma
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ÖgeFrom media-based modulation to reconfigurable intelligent surfaces: Novel index modulation solutions(Graduate School, 2022-11-11) Yiğit, Zehra ; Altunbaş, İbrahim ; Başar, Ertuğrul ; 504172313 ; Telecommunication Engineering. In these studies, we adapt the classical Hurwitz-Radon family of matrices and the new circular matrix-based STBC design to MBM in order to achieve various orders of transmission diversity gains over a single RF chain. Moreover, through extensive analyses, we obtain the theoretical bit error rate (BER) and capacity performance of the proposed schemes, which are supported via comprehensive computer simulations. In the subsequent study, we deploy an RIS with passive reflecting elements, which are capable of inducing plain phase shifts to assist the classical multiple-input multiple-output (MIMO) and IM-based MIMO transmission systems. In this study, in order to maximize the signal-to-noise (SNR) of the overall cascaded system, without applying computationally complex beamforming techniques, we propose a cosine similarity theorem-based low-complexity algorithm for adapting the phase shifts of the RIS reflecting elements. Moreover, a semi-analytical probabilistic approach is developed to derive the theoretical average bit error probability (ABEP) of the system. Furthermore, the validity of the theoretical analysis is supported through extensive computer simulations. Although a massive literature has grown up around passive RIS-aided studies, most recently, the potential of active RISs that are capable of achieving ultimate capacity gains at the expense of additional power constraints stimulates novel research domains. In that sense, we develop a novel IM scheme in which a hybrid RIS with both active and passive reflecting elements acts as a transmit information unit. In this study, according to incoming information bits, the corresponding RIS is divided into sub-groups which consist of either passive elements with simple phase shifts or active elements with adjustable amplitudes and phases in a way that each RIS realization creates a signal with clearly distinguishable magnitude. In other words, the proposed scheme constitutes a virtual amplitude shift keying (ASK) modulation. Moreover, through comprehensive theoretical analyses and computer simulations, the BER, achievable rate and energy efficiency performance of the proposed scheme are compared with existing fully passive RIS, fully active RIS and reflection modulation (RM) systems. In the last study of this thesis, in order to simplify transceiver complexity of classical multi-user transmission schemes, we propose a new over-the-air beamforming concept that completely transfers the inter-user interference cancellation duties of the transmitter to an active RIS. In the proposed concept without resorting to any hardware-complex pre/post signal processing techniques at the transmitter and the receiver, the amplitudes and phases of the active reflecting elements at the RIS are optimized to maximize sum-rate gains of a multi-user downlink transmission system. Moreover, taking inspiration from this over-the-air beamforming concept, a new receive IM scheme that transmits additional information bits to specify the index of the effective received antenna is also proposed. Contrary to the existing receive IM system designs that conduct transmit beamforming to steer the overall information to the specified received antenna, in the proposed receive IM scheme, without applying any transmit beamforming techniques, the reflection coefficients of the active RIS are adjusted to orient the overall reflected signal in direction of the effective received antenna. In these proposed over-the-air beamforming concepts, to optimize the reflection coefficients of the active RISs, two distinct semidefinite relaxation (SDR)-based optimization problems are formulated, which can be effectively solved through the CVX convex optimization toolbox. Moreover, through comprehensive simulation results, the sum-rate and BER performance of the proposed designs are investigated. In summary, this thesis presents novel IM-based physical layer solutions for future generation networks in various facets starting from the classical MBM to the emerging RIS-aided systems. Through this process, we resort to different approaches including STBC techniques, low-complexity algorithms, convex optimization, physical channel models, etc. Moreover, in order to demonstrate the performance of the systems, through comprehensive computer simulations, we compare our all system designs with the classical systems and their state-of-the-art competitors. Then, in order to support these results, we attempt to derive theoretical performance analyses.