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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 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 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 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.
