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 Interpolation based pilot-aided channel estimation for STBC spatial modulation and performance analysis under imperfect CSI(INST Engineering Technology-Iet, Michael Faraday House Six Hills Way Stevenage, Hertford Sg1 2Ay, England, 2016-09-20) Doğan, Hakan; Başar, Ertuğrul; Panayırcı, Erdal; ACAR, YUSUF; GÜNTEKİN, BAHAR; 237377; 149116; 10331A combination of space-time block coding and spatial modulation (STBC-SM) has been recently proposed for multiple input-multiple output systems to obtain both spatial diversity gain and more capacity simultaneously while assuming the perfect channel state information (P-CSI) was available at the receiver. However, in practical scenarios the CSI is unknown to the receiver and should be estimated in order to detect the transmitted data in a reliable way. Therefore, channel estimation (CE) is a major challenge in designing the STBC-SM systems. In this study, the problem of CE is investigated and a new pilot-aided channel estimation (PA-CE) technique, coupled with an interpolation, is proposed for the STBC-SM systems operating in the presence of rapidly time-varying mobile channels. Several interpolation schemes such as the linear, nearest neighbour, piecewise cubic Hermite and the low-pass interpolations are applied and their performances are compared to determine the best suitable interpolation technique to be employed in STBC-SM systems. Bit error rate (BER) performance of the proposed CE technique is then investigated in time-varying channels with different modulation. Moreover, the pairwise error probability of the STBC-SM scheme is derived and its average bit error probability is evaluated analytically in the presence of CE errors.Publication Open Access Dual-mode index modulation aided OFDM with generalized prefix(2019-06) Aldırmaz Çolak, Sultan; Cooklev, Todor; ACAR, YUSUFRecently, 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.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.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 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 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 Spline Based Channel Estimation for STBC-SM Systems over Fast-Varying Rician Fading Channels(IEEE, 345 E 47Th St, New York, Ny 10017 USA, 2015-05-16) Doğan, Hakan; Panayırcı, Erdal; ACAR, YUSUF; 237377; 10331In the STBC-SM systems, the information is carried both by STBC symbols and indices of the transmit antennas from which these symbols are transmitted. Channel estimation is a critical process at the receiver during the coherent detection of the transmitted STBC symbols and indices of the transmit antennas. In this paper, a spline interpolation and pilot symbols based channel estimation has been proposed for the space-time block coded spatial modulation (STBC-SM) systems to track the channel variations in the presence of Rician fading channels. The estimation of channel at pilot durations is done by least squares (LS) method and then the spline based channel interpolation is performed. It has been shown via computer simulations that the proposed spline based channel estimation channel estimation outperforms the piecewise linear interpolation (PLI) and the nearest neighbor interpolation (NNI) based channel estimations.Publication Metadata only Pilot symbol assisted channel estimation for 4x4 space time block coded spatial modulation systems(IEEE, 345 E 47th St, New York, Ny 10017 USA, 2015) Doğan, Hakan; Panayırcı, Erdal; ACAR, YUSUF; 237377; 10331Recently, spatial modulation (SM) and space-time block coding (STBC) are combined to take advantage of the benefits of both while avoiding their drawbacks for multiple-input and multiple-output (MIMO) systems. The pioneering works on STBC-SM assume that perfect knowledge of the channel fading coefficients is available at the receiver. This work(1) addresses the challenging and timely problem of channel estimation for 4 x 4 STBC-SM systems in the presence of time-varying channels. In this paper, the estimation of channel at pilot durations is done by least square (LS) method and then the channel interpolation is performed by linear interpolation or nearest neighbor interpolation algorithms. Simulation results have demonstrated that the proposed channel estimation based on the linear interpolation offer substantial performance gains over the channel estimation based on the nearest neighbor interpolation. In particular, a savings of about 5dB is obtained at BER = 10(-5), as compared with the nearest interpolation based receiver at 120km/h for 4 x 4 STBC-SM systems with the binary phase shift keying (BPSK) modulation.Publication Metadata only Performance Improvement for Correlated 4x4 MIMO-OFDM Systems by Generalized Prefix Approach(IEEE, 345 E 47Th St, New York, Ny 10017 Usa, 2013) Cooklev, Todor; Doğan, Hakan; Yıldız, Hakan; ACAR, YUSUF; 237377; 41066; 253657Antenna correlation limits the multiplexing gain achieved by practical MIMO-OFDM systems and degrades the performance significantly. Recently, investigations are focused to reduce the antenna correlation by the designing new antenna structures. Differently, in this paper, we propose the generalized prefix approach to solve problem for correlated MIMO-OFDM system. It is shown that the proposed generalized prefix for 4x4 MIMO-OFDM exhibits a gain of about 8 dB over the conventional 4x4 MIMO-OFDM system at BER = 10(-4)