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Öğe Differential modulation based network coded cooperative communications [Farksal Modülasyon Kullanan A? Kodlamali Işbirlikli Iletişim](Institute of Electrical and Electronics Engineers Inc., 2015) Karabulut M.A.; Ilhan H.; Özdemir O.Multiple access relay channel (MARC) where multiple users communicate with a common destination via a relay, is an innovative approach and one of the most important network coding applications in wireless cooperative communications in recent years. In this paper, noncoherent differential binary phase shift keying (DPSK) technique which eliminates the need for channel estimation cost is applied to the MARC system model that uses maximum likelihood detection approach at the common destination. Noncoherent DPSK modulation of the MARC system model provides full diversity gain that has been observed at the resulting Monte-Carlo simulation. © 2015 IEEE.Öğe Hemorrhagic bowel syndrome in a holstein cow - case report(Veteriner Fakultesi Dergisi, 2012) Kemal Çiftçi M.; Yavuz O.; Hatipoğlu F.; Özdemir O.In this report, hemorrhagic bowel syndrome (HBS) was defined pathologically for the first time in Turkey in a Holstein dairy cow. It was reported that a 4-year-old cow died suddenly with symptoms of loss of appetite, decreased milk yield, dehydration, and abdominal bloating in a dairy farm. Grossly, serosa of jejunum was observed with dark red color and its lumen was completely filled with blood clots. Some parts of jejunum lumen were narrowed due to submucosal and intramural bleeding. Microscopically, necro-hemorrhagic enteritis, and eosinophilic granulocyte and mononuclear cell infiltrations with extensive submucosal hemorrhages were observed. In addition, Gram-positive, rod-shaped and endospore-forming bacteria were seen intensively around of bleeding areas in the lamina propria. The death was concluded to be associated with HBS by macroscopic and microscopic findings, characteristic for the syndrome and in accordance with the literature evaluating this case. HBS causes significant losses in dairy cattle in many countries of the world. This report aimed to point out the importance of the topic, which is the first case report of HBS in Turkey, where dairy cow enterprises are growing rapidly.Öğe Implementation of cooperative communications using ultrasonic wireless terminals [Ses-üstü telsi?z termi?naller kullanilarak i?şbi?rli?kli? i?leti?şi?mi?n gerçekleşti?ri?lmesi?](2011) Özdemir O.; Yilmaz A.O.; Herdem S.In this paper, an experimental framework that enables observing the performance improvements provided by cooperative diversity schemes is introduced. Unlike the RF based test-beds proposed in the literature, a wireless network consisting of ultrasonic terminals has been implemented. It has been shown that terrestrial applications of the ultrasonic communications provide an effective computer-aided experiment environment on which various cooperative physical layer protocols can be tested. Using this empirical setup, a digital relaying based bi-directional communication scenario has been examined where two users exchange information by employing differential binary modulation and network coding via a relay. The direct and relayed bit-wise XOR-ed and differential encoded signals are combined based on maximum likelihood (ML) detection at the receivers to prevent performance loss due to error propagation. Bit Error Rate (BER) measurement results have verified the theoretical studies in the literature by demonstrating that full diversity order is obtained. © 2011 IEEE.Öğe Relaying selection based multiple access relay channel [Röle Seçimli Çoklu Erişim Röle Kanali](Institute of Electrical and Electronics Engineers Inc., 2016) Karabulut M.A.; Özdemir O.; Ilhan H.Relay selection in case of fast cascade Rayleigh fading channels has been examined in multiple access relay channel structure which is one of the high spectral efficiency network coding applications. Error performance analysis of MARC system has been made for noncoherent binary frequency shift keying (BFSK) and it has been shown that the proposed approach provides full diversity gain. © 2016 IEEE.Öğe SNR-based antenna selection with threshold value in wireless channels [Telsiz kanallarda esik degerlikli SNR-tabanli anten seçimi](2013) Aydin E.; Ilhan H.; Özdemir O.In this study, in order to reduce the end-to-end bit error rate (BER) at the destination, two different antenna selection models based on signal to noise ratio (SNR) have been proposed. Relay node contains multiple antennas and BPSK modulation is used. In these models under consideration, different optimal decision rule is determined theoretically. To generate each threshold decision rule, either instantaneous and average SNR or both together in S?D, S?R and R?D links are used. Proposed antenna selection algorithm with the optimal threshold value can reduce significantly the end-to-end BER according to the simple relaying technique. © 2013 IEEE.Öğe User selective relaying in multiple access relay channels(2012) Özdemir O.Network coding has recently received significant attention as an innovative approach to improve the throughput of wireless communication systems. The multiple access relay channel (MARC), in which multiple users communicate with a common destination via a relay, is one of the important network coding applications for wireless cooperative communications. In this paper, selective relaying approach which combats performance degradation due to error propagation in digital relaying based wireless networks has been adopted to the MARC model. In the proposed scheme, the information of the some of the user terminals are transmitted to the destination through both direct and relay channel utilizing ideas from network coding while the other terminals employ only the direct link. The optimal subset of all user terminals whose transmissions will be listened and retransmitted by the relay are determined by the destination terminal in a manner to minimize the overall end to end bit error rate of the system and sent to the relay through the feedback link. Simulation results for Rayleigh fading channels show that the proposed selection relaying scheme outperform the noncooperative system that involves direct transmissions and overcome the diversity gain reduction due to error propagation. © 2012 University of Split.Öğe Virtual noise based detection in cooperative systems with co-channel interference [Ortak Kanal Girişimi Bulunan Işbirlikli Sistemlerde Sanal Gürültüye Dayali Sezim](Institute of Electrical and Electronics Engineers Inc., 2016) Aslan H.; Ilhan H.; Özdemir O.In this paper, we have investigated the effect of cochannel interference on Decode-and-forward based cooperative communication system by providing the analytical results and computer simulations over Rayleigh fading channels. Virtual noise technique is used with co-channel interference at relay and destination terminals. It can be clearly observed that virtual noise techniques provides full diversity gain for proposed system. The accuracy of the analytical results shown by computer simulations. © 2016 IEEE.
