Browsing by Author "Basaran,M."

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Citation Count: 0
Atmosferik Türbülans Altinda Orbital Açisal Momentum Tabanli Haberleşme Sistemleri Orbital Angular Momentum Based Communication Systems under Atmospheric Turbulence;
(Institute of Electrical and Electronics Engineers Inc., 2020) Sheikh,A.A.A.; Basaran,M.; Erkucuk,S.
Orbital Angular Momentum (OAM) may be a candidate for future communication systems due to its advantages in terms of high data rates and effective frequency utilization. OAM can provide a solution where a beam is transformed into multiple beams within itself and becomes independent streams of data (pertaining to the principle of orthogonality) to be transferred when properly utilized. However, the free space contains atmospheric turbulence which interferes with the beam propagation of OAM and as a result the photons in the light beam are affected as well as the independence of each OAM mode. Therefore, the data stream suffers crosstalk. In this study, weak and strong atmospheric turbulences and how they affect a variety of OAM modes as they propagate through free space are investigated, and important OAM implementation issues are discussed. © 2020 IEEE.
Citation Count: 17
Channel Estimation for TDS-OFDM Systems in Rapidly Time-Varying Mobile Channels
(Institute of Electrical and Electronics Engineers Inc., 2018) Şenol, Habib; Erküçük, Serhat; Erküçük,S.; Çirpan,H.A.
This paper explores the performance of time-domain synchronous orthogonal frequency-division multiplexing (TDS-OFDM) systems operated under rapidly time-varying mobile channels. Since a rapidly time-varying channel contains more unknown channel coefficients than the number of observations, the mobile channel can conveniently be modeled with the discrete Legendre polynomial basis expansion model to reduce the number of unknowns. The linear minimum mean square error (LMMSE) estimate can be exploited for channel estimation on inter-block-interference-free received signal samples owing to transmitting pseudo-noise (PN) sequences. In conventional TDS-OFDM systems, the channel estimation performance is limited due to estimating channel responses only from the beginning part of the channel. Therefore, a new system model named "partitioned TDS-OFDM system" is proposed to improve the system performance by inserting multiple PN sequences to the middle and end parts of the channel as well. In addition to providing the reconstruction error performance, Bayesian Cramer-Rao lower bound is derived analytically. Also, the LMMSE-based symbol detection is employed. To alleviate the negative effects of inter-carrier-interference (ICI) occuring in mobile channels, ICI cancellation is applied to enhance the detection performance. The simulation results demonstrate that the proposed TDS-OFDM system is superior to the conventional system and its corresponding performance is able to approach the achievable lower performance bound. © 2018 IEEE.