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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, HakanFocusing 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.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 BinboğaIn 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.Yayın A computer-aided design technique for lossless matching networks with mixed, lumped and distributed elements(Elsevier GMBH, 2004) Sertbaş, Ahmet; Yarman, Bekir Sıddık BinboğaA computer-aided method for the design of lossless broadband matching networks with lumped elements and commensurate transmission lines is presented. ne method is based on combining the simplifield real frequency technique with the algebraic network decomposition by Fettweis. To show the application of the Computer-Aided Design (CAD) approach, an UHF antenna matching problem is solved.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 BinboğaDesign 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.Yayın A real frequency approach to describe lossless two-ports formed with mixed lumped and distributed elements(Urban & Fischer Verlag, 2001) Aksen, Ahmet; Yarman, Bekir Sıddık BinboğaThe design of microwave filters, matching networks, amplifiers, that Is the "Broadband Networks" with mixed lossless lumped and distributed elements, has been a significant concern of the circuit theoreticians of the field. Yet, there has been no complete practical solution Introduced In the literature so far. In this paper, an attempt has been made to design broadband networks constructed with a cascade connection of low pass LC ladders connected with commensurate transmission lines. The new design procedure Is based on the two-variable description of the Simplified Real Frequency Technique. Up to five mixed-elements explicit equations are given to describe some selected network topologies. In general, synthesis Is carried out employing a decomposition technique first Introduced by Alfred Fettwels. A "Double Matching Design" example is presented to exhibit the merits and the application of the new approach.Yayın Wideband matching network design for a V-Shaped square monopole antenna using Real Frequency Technique(IEEE, 2013) Köprü, Ramazan; Aydın, Çağatay; Atilla, Doğu Çağdaş; Karakuş, Cahit; Yarman, Bekir Sıddık BinboğaIn this paper, design and simulation of a wideband matching network for a broadband V-shaped square monopole antenna is presented. Matching network design is unavoidable in most cases even vital to facilitate a maximally flat power transfer gain for an antenna. In the work, the matching network design is done for a particular square monopole antenna with V-shaped coupling element that has essentially bandwidth increasing effect. The V-shaped antenna had been manufactured, tested and analyzed elaborately in a previous work. With this work, it is now equipped by a matching network. 'Real Frequency Technique' (RFT) is employed in matching network design.Yayın On the cyclostationary statistics of ultra-wideband signals in the presence of timing and frequency jitter(Elsevier GMBH, Urban & Fischer Verlag, 2008) Öner, Mustafa MengüçCyclostationarity is an inherent characteristic of many man-made communication signals, which, if properly recognized, can be exploited for performing various signal-processing tasks. Determining the cyclostationary characteristics of a signal of interest is the first step in the design of signal processing systems exploiting this cyclostationary behaviour. This paper investigates the cyclostationary statistics of various signalling schemes employed in ultra-wideband (UWB) communication systems. Analytical expressions are derived for the cyclic autocorrelation and spectral correlation density functions in the presence of random timing and frequency jitter, which are characterized by discrete-time stationary random processes with known distribution functions.Yayın Richards uzayında band geçiren devre fonksiyonu gerçeklemesi ve yama anten uyumlaştırmada kullanımı(IEEE, 2014-04-23) Köprü, Ramazan; Aydın, Çağatay; Yarman, Bekir Sıddık BinboğaLiteratürde 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.
