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2004 - 200912010 - 20153
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Scopus Q: N/A × Konu: Broadband networks ×

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Listeleniyor 1 - 4 / 4
  • Küçük Resim
    Yayın
    Iterative channel estimation approach for space-time/frequency coded OFDM systems with transmitter diversity
    (Assoc Elettrotecnica Ed Elettronica Italiana, 2004-06) Çırpan, Hakan Ali; Panayırcı, Erdal; Doğan, Hakan
    Focusing on transmit diversity orthogonal frequency division multiplexing (OFDM) transmission through frequency selective channels, this paper pursues novel iterative channel estimation approaches for both space-frequency OFDM (SF-OFDM) and space-time OFDM (ST-OFDM) systems. Relying on the unifying signal model for SF-OFDM and ST-OFDM transmitter diversity systems, we develop computationally efficient, maximum a posteriori (MAP) channel estimation algorithms according to the MAP criterion. The algorithms require a convenient representation of the discrete multipath fading channel based on the Karhunen-Loeve (KL) orthogonal expansion and estimates the complex channel parameters of each subcarriers iteratively using the expectation-maximisation (EM) method. In order to explore the performance, the closed-form expression for the average symbol error rate (SER) probability is derived for the maximum ratio combiner (MRC). Furthermore, to benchmark performance of the MAP channel estimator, the modified Cramer-Rao bound of channel estimates is also derived. Finally, we provide simulation results studying the influence of delay spread, propagation parameters and modelling mismatch on the performance of channel estimation techniques. Simulation results confirm our theoretical analysis and illustrate that the proposed algorithms are capable of tracking fast fading and improving overall performance.
  • Küçük Resim
    Yayın
    Transformerless bandpass matching network design for Y-Shaped monopole antenna
    (IEEE, 2015) Aydın, Çağatay; Atilla, Doğu Çağdaş; Karakuş, Cahit; Köprü, Ramazan; Yarman, Bekir Sıddık Binboğa
    In this paper, a transformerless bandpass matching network design procedure is presented. The Real Frequency Techniques are powerful numerical methods to design wideband lossless 2-port networks such that filters and matching networks. In these techniques, the value of the termination resistance of the designed network could not be yielded as 50 ohm by numerical package. Hence, a transformer is also required for 50 ohm termination which is not practical for high frequency applications. Also in this study a novel wideband monopole antenna is presented. The proposed antenna is consisting of two major elements; Y-shaped impedance matching plate and hemi-circular radiator. Moreover Y-shaped impedance matching plate connected to a feeding probe excites the suspended hemi-circular radiator via air gap. and its frequency band is expanded by using transformerless bandpass design procedure.
  • Küçük Resim
    Yayın
    Unit element bandpass filter design via simplified real frequency technique for UWB microstrip patch antenna
    (IEEE Computer Society, 2014) Köprü, Ramazan; Kılınç, Sedat; Aksen, Ahmet; Yarman, Bekir Sıddık Binboğa
    Design of a UWB (Ultra Wideband) microstrip patch antenna to operate in the first channel of the UWB standard and a bandpass (BP) UE (Unit Element) microstrip filter (BPUEF) for this antenna are studied and presented with promising experimental results. A typical UE BP filter is a lossless 2-port network which is formed with certain number of cascade connected commensurate transmission lines. Based on the simplified real frequency technique (SRFT) in Richards domain, driving point Darlington impedance function of the BPUEF is obtained via optimization such that optimum power transfer would be possible between a PA (power amplifier) and the antenna. Using the UE synthesis, characteristic impedance values of each UE is extracted from the input impedance function. Theoretical design (Matlab), simulation (ADS, Agilent Inc.) and the measurements are shown to be in a high degree of agreement.
  • Küçük Resim
    Yayın
    Richards uzayında band geçiren devre fonksiyonu gerçeklemesi ve yama anten uyumlaştırmada kullanımı
    (IEEE, 2014-04-23) Köprü, Ramazan; Aydın, Çağatay; Yarman, Bekir Sıddık Binboğa
    Literatürde çok iyi bilinmektedir ki, Richards-düzlemi, Laplace-düzleminde tanjant hiperbolik eşlemesi uygulanarak elde edilen dönüştürülmüş bir uzaydır. Richards frekansı cinsinden üretilen devre fonksiyonları gerçek frekans ekseninde π periyoduna sahiptir. Richards uzayında alçak geçiren prototip devre fonksiyonu tasarlandığında, bu periyodik özellik nedeniyle, karşı gelen periyodik band geçiren devre fonksiyonu frekans ekseninde belirli bandlarda tekrarlanarak ortaya çıkmaktadır. Tasarımcı, uygulamanın gereksinimlerine göre bu tekrarlanan bandlar arasından ilgilendiği bandı seçebilir. Bu çalışmada, 3.2448-3.744 GHz bandında çalıştırılmak üzere tasarlanmış UWB uygulamaları için elverişli bir mikroşerit yama anten için eş-uzunluklu (commensurate) iletim hatları ile oluşturulmuş uyumlaştırma devresi tasarımı ele alınmaktadır. Tasarımda, SRFT (Simplified Real Frequency Technique: Basitleştirilmiş Gerçel Frekans Tekniği) kullanılmaktadır ve teorik tasarım ile MWO (AWR) benzeşimleri arasında çok iyi uyum olduğu gözlenmiştir.