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ACAR, YUSUF

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Dr. Öğr. Üyesi

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ACAR

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YUSUF

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2016 - 20195
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Now showing 1 - 5 of 5
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    PublicationOpen Access
    Dual-mode index modulation aided OFDM with generalized prefix
    (2019-06) Aldırmaz Çolak, Sultan; Cooklev, Todor; ACAR, YUSUF
    Recently, a dual-mode OFDM relying on index modulation (DM-OFDM-IM) has been introduced to increase the data rate of the conventional IM based OFDM techniques. However, such a mechanism has bit error rate performance loss due to the deep fading channels such as the practical Rayleigh channels. In this work, to improve the BER performance of the DM-OFDM-IM technique, a new technique, that is called as DM-OFDM-IM with generalized prefix (DM-OFDM-IM-GP) is proposed. The simulation results illustrate that the proposed DM-OFDM-IM with GP achieves about 10 dB SNR gain over the existing DM-OFDM-IM at the spectral efficiency of 4, 2.22 and 1.33 bits/s/Hz in Rayleigh fading channel. Keywords-Index Modulation; Generalized Prefix; Orthogonal Frequency Division Multiplexing; Dual-Mode, Index Modulation, Spatial Modulation.
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    PublicationOpen Access
    Channel estimation for OFDM-IM systems
    (2019) Aldırmaz Çolak, sultan; Başar, Ertuğrul; ACAR, YUSUF
    Orthogonal 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.
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    PublicationEmbargo
    Data detection based iterative channel estimation for coded SM-OFDM systems
    (IEEE, 345 E 47Th St, New York, Ny 10017 USA, 2016) Leblebici, Mehmet Merih; Doğan, Hakan; Panayırcı, Erdal; ACAR, YUSUF; 237377; 249850; 10331
    The combination of spatial modulation (SM) and orthogonal frequency division multiplexing (OFDM) as SM-OFDM is a recently proposed efficient modulation scheme with exploiting the index of transmit antenna to convey information bits for multiple-input multiple-output (MIMO) wireless communication systems due to its low complexity feature. The pioneering works assume that the perfect channel state information (P-CSI) or pilot symbols aided channel estimation (PSA-CE) is available at the receiver. The open question is whether the accuracy of pilot based channel estimation is satisfactory to accomplish high data rate transmission in SM-OFDM systems. This paper explores the iterative channel estimation (ICE) problem for the coded SM-OFDM systems. We showed that the quality of the channel estimation can be further enhanced by the detection of symbols at the receiver. Through comparative simulations, we show that the proposed ICE method has notable bit error rate (BER) performance compared with the PSA-CE method for the binary phase shift keying (BPSK) modulation over the typical urban (TU) channel model.
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    PublicationOpen Access
    Novel OFDM System Using Orthogonal Pilot Symbols with Subcarrier Index Modulation
    (Bajece (İstanbul Teknik Üniversitesi), 2019) ACAR, YUSUF; Çolak, S. Aldırmaz
    In 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.
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    PublicationOpen Access
    Sub-Block Aided OFDM with Index Modulation
    (Bajece (İstanbul Teknik Üniversitesi), 2019) ACAR, YUSUF
    Recently, orthogonal frequency division multiplexing (OFDM) with index modulation (IM) has been appeared as a novel method for future wireless communication systems. However, such a mechanism has low spectral efficiency since some sub-carriers are not activated in order to implicitly convey information. In this paper, a subblock dependent approach, called sub-block aided OFDMIM (SA-OFDM-IM) technique, is proposed for spectral efficiency enhancement of the OFDM-IM method with lower complexity. The simulation results illustrate that the proposed SA-OFDM-IM and well known OFDM-IM have same bit error rate (BER) performance while SA-OFDMIM has 40% more spectral efficiency with low complexity.