Elektrik-Elektronik Mühendisliği Bölümü / Department of Electrical and Electronics Engineering
Permanent URI for this collectionhttps://hdl.handle.net/11413/6818
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Browsing Elektrik-Elektronik Mühendisliği Bölümü / Department of Electrical and Electronics Engineering by Author "Başar, Ertuğrul"
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Publication Adaptive dual-mode OFDM with index modulation(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2018-10) Aldırmaz Çolak, Sultan; Başar, Ertuğrul; ACAR, YUSUF; 41633; 237377; 149116With the integration of the index modulation concept, the popular OFDM has gained an appealing new dimension. However, OFDM with index modulation (OFDM-IM) causes a decrease in data rate for higher order modulations due to its unused subcarriers. Recently, dual-mode OFDM with index modulation (DM-OFDM-IM) has been proposed to prevent this decrease in data rate. The spectral efficiency (SE) of both techniques depends on the selection of different parameters, such as modulation types and number of active subcarriers. However, the quality of the wireless channel has not been taken into account yet to increase the data rate. In this paper, we propose a new adaptive DM-OFDM-IM (A-DM-OFDM-IM) system to enhance the bit error probability (BER) performance considering the channel conditions and obtain a substantial increase in SE. Unlike the previous DM-OFDM-IM and the classical OFDM-IM schemes, our proposed system enables the use of different types of modulations for different subblocks in one OFDM signal. We demonstrate that the SE of the proposed system is comparable with that of its OFDM-IM and DM-OFDM-IM counterpart under frequency selective Rayleigh channels. Moreover, computer simulations corroborate that the derived theoretical results are considerably accurate for the SE of A-DM-OFDM-IM systems. (C) 2018 Elsevier B.V. All rights reserved.Publication 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.