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 Metadata only Channel estimation for spatial modulation orthogonal frequency division multiplexing systems(IEEE, 345 E 47th St, New York, Ny 10017 USA, 2015-10-14) Doğan, Hakan; Panayırcı, Erdal; ACAR, YUSUF; 237377; 10331A combination of spatial modulation and orthogonal frequency division multiplexing (SM-OFDM) has been recently proposed for multicarrier systems while assuming the perfect channel state information (P-CSI) available at the receiver. But, in practical scenarios, the estimation of CSI is crucial in order to detect the transmitted data coherently. In this work(1), a new frame structure and pilot symbol aided channel estimation (PSA-CE) technique with a piecewise linear interpolation is proposed for the SM-OFDM systems operating in the presence of frequency selective channel. Bit error rate (BER) performance of the proposed channel estimation technique is then investigated with different channel models such as Typical Urban ( TU) and Rural Urban (RU) for 4-quadrature amplitude modulation (QAM). In particular, it is shown that the performance with estimated channel came close to that with known channel within 2.3 dB in SNR for BER = 10(-4) for TU channels.Publication Metadata only High-Performance Mimo Ofdm Wireless Systems With Generalized Prefix(IEEE, 345 E 47Th St, New York, Ny 10017 Usa, 2013) Yıldız, Hakan; Cooklev, Todor; Doğan, Hakan; ACAR, YUSUF; 237377; 41066Consumers require increasing data rates and therefore it is important to develop techniques that increase the spectrum efficiency. MIMO OFDM is a fundamental technology for high data rate wireless systems. Correlation among the different spatial streams is the main factor limiting the spectral efficiency. All practical MIMO OFDM wireless systems use cyclic prefix (CP). In this paper we propose a novel prefix for MIMO OFDM wireless systems, referred to as generalized prefix. This generalized prefix provides additional degree of freedom, which can be optimized and provides improved performance for correlated MIMO channels.Publication Metadata only High performance OFDM with index modulation(2019-02) Cooklev, Todor; ACAR, YUSUFOrthogonal frequency division multiplexing (OFDM) with index modulation (OFDM-IM), which has been recently proposed as an alternative waveform to classical OFDM, generally achieves lower bit error rate compared to classical OFDM because it is more robust to bit errors by encoding the information in the location of the active subcarriers instead of only modulating the subcarriers. In this paper, we propose a higher-performance OFDM-IM scheme. The proposed system is more reliable than OFDM-IM, particularly for channels that have deep fading. The proposed system uses generalized prefix (GP) as a guard interval and this GP provides additional degrees of freedom, which can be optimized. Comprehensive computer simulation results are included to demonstrate the significant performance improvement for different channel models, such as deep Rayleigh fading and realistic channels with high mobility. (C) 2018 Published by Elsevier B.V.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 Embargo 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; 10331The 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.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 Pilot symbol aided channel estimation for spatial modulation-OFDM systems and its performance analysis with different types of interpolations(Springer, 233 Spring St, New York, Ny 10013 USA, 2017-06) Doğan, Hakan; Panayırcı, Erdal; ACAR, YUSUF; 237377; 10331Spatial modulation orthogonal frequency division multiplexing (SM-OFDM) system has been recently proposed as an alternative for multiple-input multiple-output (MIMO)-OFDM systems to increase spectral efficiency by keeping a low-complexity implementation. In the literature, SM-OFDM systems assume a perfect channel state information (P-CSI) available at the receiver for coherent detection and the channel estimation problem is not considered. It is clear that the channel estimation is a critical issue on the performance of SM-OFDM systems. In this paper, a frame structure where pilot symbols are typically interspersed with data symbols among the sub-carriers to aid the channel estimation is considered. Then the pilot symbol aided channel estimation (PSA-CE) technique with different interpolations is proposed for the SM-OFDM systems. It is shown that in the proposed PSA-CE, equidistantly spaced pilot symbols allow to reconstruct the channel response by means of interpolation if the spacing of the pilots is sufficiently close to satisfy the sampling theorem. Linear, nearest neighbor, piecewise cubic Hermite and the low-pass interpolations are investigated to explore trade-off between complexity and performances. We show that the low pass interpolator yields better performance than the other interpolation techniques for selected cases such as higher order modulations. The results validate the potential of the proposed PSA-CE estimation applying to SM-OFDM systems.Publication Open Access Sub-Block Aided OFDM with Index Modulation(Bajece (İstanbul Teknik Üniversitesi), 2019) ACAR, YUSUFRecently, 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.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 Metadata only Generalised prefix for space-time block-coded orthogonal frequency division multiplexing wireless systems over correlated multiple-input multiple-output channels(Inst Engineering Technology-Iet, Michael Faraday House Sıx Hılls Way Stevenage, Hertford Sg1 2Ay, England, 2014-06-12) Yıldız, Hakan; Cooklev, Todor; Doğan, Hakan; ACAR, YUSUF; 253657; 237377; 41066Space-time block coding (STBC) orthogonal frequency division multiplexing (OFDM) is known to improve the reliability of broadband communication over wireless links. However, this technique suffers from a performance loss when the multiple-input multiple-output (MIMO) channel is correlated. This study addresses this problem. A STBC-OFDM system is proposed that is based on convolution that is skew-circular, rather than circular. This skew-circular convolution leads to one additional degree of freedom. The additional parameter can be optimised leading to improved performance for MIMO channels that are correlated. The skew-circular convolution is achieved via the introduction of a generalised prefix. The simulation results are given, illustrating the performance improvement of the proposed STBC-OFDM system. Furthermore, the proposed system is shown to be robust when channel state information is known not precisely, but imperfectly.