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Öğe Antenna selection for decode and forward based MIMO cooperative networks [Çöz ve ilet temelli MIMO işbirlikli a?lar için anten seçimi](IEEE Computer Society, 2014) Aydin E.; Ilhan H.; Özdemir Ö.In this paper, a cooperative system structure that utilizes decode and forward (DF) method with antenna selection based on the signal to noise ratio (SNR) have been proposed. In order to decrease performance degradation due to error propagations in DF based wireless cooperative networks and increase the error performance of the system, selection combining (SC), classical maximal ratio combining (MRC), cooperative-maximal ratio combining (C-MRC) and link adaptive regeneration (LAR) techniques have been utilized at destination. Error performance analyses of the considered structures are investigated using optimal decision rules determined theoretically for the corresponding relaying strategy. © 2014 IEEE.Öğe Error performance analysis of decode and forward based cooperative systems with relay selection [Çöz ve ilet tabanli röle seçimli isbirlikli sistemlerin hata performans analizi](2013) Ipek Akin A.; Ilhan H.; Özdemir Ö.In this paper, error performance analysis of a cooperative system with relay selection that utilizes decode and forward (DF) method is considered. The source-relay, relay-destination and source-destination links are modeled as Nakagami-m distributed random variables. The effects of the cooperative maximal ratio combining (C-MRC) used to decrease performance degradation due to error propagation in DF based wireless cooperative networks and classical maximal ratio combining (MRC) methods on error performance of the system are investigated with computer simulations. It has been shown that C-MRC technique provides significant performance improvement with respect to the MRC method. © 2013 IEEE.Öğe Fomes fomentarius and tricholoma anatolicum (Agaricomycetes) extracts exhibit significant multiple drug-resistant modulation activity in drug-resistant breast cancer cells(Begell House Inc., 2020) Doğan H.H.; Kars M.D.; Özdemir Ö.; Gündüz U.Multiple drug resistance is one of the main problems that hinder successful cancer chemotherapy. Investigations on the development of effective chemotherapeutic agents and drug resistance inhibitors motivate studies on the effects of natural compounds on drug-resistant cancer cells. For this purpose, aqueous, methanol, and ethanol extracts of Fomes fomentarius and Tricholoma anatolicum were prepared. The extracts were evaluated to assess their anticancer and multiple drug resistance modulation activities. Cytotoxic effects of F. fomentarius and T. anatolicum extracts on paclitaxel and vincristine resistant P-glycoprotein over-expressing MCF-7 cell lines were investigated by cytotoxicity test (XTT). P-glycoprotein reversing ability and MDR modulation effects of the extracts were determined by flow cytometry through Rhodamine 123 exclusion assay. Furthermore, 11 phenolic compounds in the extracts were characterized by HPLC. As a result of the cytotoxicity assay, IC50 values of the extracts for MCF-7/Vinc were between 1.08 and 1.80 mg/ mL, and IC50 values for MCF-7/Pac were found between 1.11 and 2.83 mg/mL. Strikingly, methanol extract of F. fomentarius and ethanol extract of T. anatolicum have potential value to become MDR reversing agents for drug-resistant breast cancer cells. © 2020 by Begell House.Öğe Joint network-channel coding with C-MRC based demodulate and forward protocol in two-way relay channels [C-MRC tabanli kipleme çöz ve i?let protokolü ile i?ki yönlü röleli kanallarda birleşik a?-kanal kodlamasi](2010) Özdemir Ö.; Yilmaz A.Ö.Research activities to reduce the system complexity and energy consumption of digital relaying based cooperative wireless networks have yielded the demodulate-forward scheme where the relay performs demodulation, instead of decoding, on the received signals. On the other hand, cooperative maximum ratio combining (C-MRC) is another high-performance low-complexity technique used to combat error propagation in digital relaying without exploiting CRC codes which decreases the transmission efficiency. In this study, we propose a C-MRC based demodulate and forward protocol for two-way relay channels where two users exchange information via a relay. The transmission is divided into three phases in time where the first and second phases are allocated to the transmissions of uncoded or convolutionally encoded data of the users. After demodulation, the relay broadcasts the bit-wise XOR-ed packet to the users in the third phase. The numerical results for Rayleigh fading show that the proposed approach provides full diversity gain. ©2010 IEEE.Öğe Link adaptive relaying with virtual noise based detection in cooperative wireless networks [Isbirlikli telsiz aglarda sanal gürültüye dayali sezim ile link uyarlamali iletim](2013) Bozdag A.; Ilhan H.; Özdemir Ö.Cooperative communication is an approach that provides diversity gain in wireless communications systems by eliminating the requirement of locating physical antenna arrays at terminals. In this study, a scheme that combines link adaptive relaying (LAR) and virtual noise modeling based detection techniques which have been introduced in the literature to prevent performance degradation in decode and forward based cooperative wireless networks due to error propagation is proposed and its error performance is investigated for Nakagami-m channels. It has been shown by simulation results that the proposed system provides significant performance improvement in various situations with respect to the classcial LAR structures in which maximal ratio combining is employed at the destination. © 2013 IEEE.Öğe Mitigating error propagation in multiple access relay channels [Çoklu erisim röle kanalinda hata yayilimi ile mücadele](2013) Özdemir Ö.Network coding has recently received significant attention as an innovative approach that improves the spectral efficiency of wireless communication systems. The multiple access relay channel (MARC) where multiple users communicate with a common destination via a relay, is one of the important network coding applications in wireless cooperative communications. In this paper, selective relaying (SR) and maximum likelihood (ML) detection approach which combat performance degradation due to error propagation in digital relaying based wireless networks have been applied to the MARC model. Simulation results for Rayleigh fading channels show that both SR and ML detection schemes outperform the noncooperative system that involves direct transmissions and overcome the diversity gain reduction due to error propagation. © 2013 IEEE.
