Person: ACAR, YUSUF
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Dr. Öğr. Üyesi
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ACAR
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YUSUF
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Publication Open Access Channel estimation for OFDM-IM systems(2019) Aldırmaz Çolak, sultan; Başar, Ertuğrul; ACAR, YUSUFOrthogonal frequency division multiplexing with index modulation (OFDM-IM) has been recently proposed to increase the spectral efficiency and improve the error performance of multicarrier communication systems. However, all the OFDM-IM systems assume that the perfect channel state information is available at the receiver. Nevertheless, channel estimation is a challenging problem in practical wireless communication systems for coherent detection at the receiver. In this paper, a novel method based on the pilot symbol-aided channel estimation technique is proposed and evaluated for OFDM-IM systems. Pilot symbols, which are placed equidistantly, allow the regeneration of the response of the channel so that pilot symbol spacing can fulfill the sampling theorem criterion. Our results shows that the low-pass interpolation and SPLINE techniques perform the best among all the channel estimation algorithms in terms of bit error rate and mean square error performance.Publication Open Access Novel OFDM System Using Orthogonal Pilot Symbols with Subcarrier Index Modulation(Bajece (İstanbul Teknik Üniversitesi), 2019) ACAR, YUSUF; Çolak, S. AldırmazIn this work, two new transmission schemes are proposed to increase the spectral efficiency of orthogonal frequency division multiplexing (OFDM). In practical OFDM systems, channel estimation is usually performed by employing pilot symbols which is based on inserting known symbols in the time-frequency domain. However, pilot symbol designing is one of the bottlenecks of OFDM systems limiting the increase of spectral efficiency. We apply new pilot design structures, which are use orthogonal Walsh-Hadamard codes. To increase the spectral efficiency of OFDM systems, we assign the extra bits to the index of the each orthogonal Walsh-Hadamard codes. Simulation and theoretical results show that proposed methods have better performance than conventional OFDM with higher spectral efficiency. Moreover, no more energy is spent for additional information carried in the indices compared to classical OFDM systems. As a result, proposed methods provide both spectral efficiency and energy efficiency.Publication Metadata only Channel Estimation for SM Systems over Time-Varying Rayleigh Fading Channels(IEEE, 345 E 47Th St, New York, Ny 10017 Usa, 2014) Doğan, Hakan; Panayırcı, Erdal; ACAR, YUSUF; 237377; 41066; 10331This paper is concerned with the challenging and timely problem of channel estimation for spatial modulated systems in the presence of time varying channels. Recently, estimation of channel state information for SM systems is investigated by the recursive least square (RLS) algorithm for slow fading channels. However, it is clear that the RLS based receiver will have a performance degradation for fast fading channels. Therefore, we developed iterative channel estimation based on detected symbols and curve fitting to track the channel variations for SM systems. Simulation results have demonstrated that the proposed iterative channel estimation offer substantial performance gains over the RLS channel estimation. In particular, a savings of about 4dB is obtained at BER = 10(-7), as compared with RLS based receiver at 150km/h for 2 x 4 single carrier SM systems.Publication Metadata only Iterative Channel Estimation For Spatial Modulation Systems Over Fast Fading Channels(IEEE, 345 E 47Th St, New York, Ny 10017 Usa, 2014) Doğan, Hakan; Panayırcı, Erdal; ACAR, YUSUF; 237377; 41066; 10331Spatial Modulation (SM) based on the use of antenna indices to transmit information in addition to the conventional signal constellations has been recently proposed to solve practical problems encountered in MIMO systems. In the literature, estimation of CSI for SM systems is simply investigated by RLS for slow fading channels. However, iterative receivers that offer significant performance gains over a non- iterative when the total number of pilot is not sufficient and the channel is fast fading have not been investigated for SM based systems. In this paper, it shown that the RLS based receiver has a performance degradation for fast fading channels and a new iterative channel estimation techniques is proposed with the necessary signal model to enhance receiver performance for fast fading channels. Computer simulation results indicate that proposed iterative receiver has a significant performance advantage over the RLS based receiver for time-varying Rayleigh channels.