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Yayın On the extraction of the channel allocation information in spectrum pooling systems(IEEE, 2007-04) Öner, Mustafa Mengüç; Jondral, Friedrich K.The spectrum pooling strategy allows a license owner to share a part of his licensed spectrum with a secondary wireless system (the rental system, RS) during its idle times. The coexistence of two mobile systems on the same frequency band poses many new challenges, one of which is the reliable extraction of the channel allocation information (CAI), i.e. the channel occupation of the licensed system (LS). This paper presents a strategy for the extraction of the CAI based on exploiting the distinct cyclostationary characteristics of the LS and RS signals and demonstrates, via simulations, its application on a specific spectrum pooling scenario, where the LS is a GSM network and the RS is an OFDM based WLAN system.Yayın Classification-based macroblock layer rate control for low delay transmission of H.263 video(IS & T - Soc Imaging Science Technology, 2003-07) Bayazıt, UluğPuri and Aravind's method of macroblock bit count estimation for video rate control is based on the classification of the macroblock data into discrete classes and assigning a unique non-linear estimate for each class and quantization parameter pair. This method stands apart from other methods in the literature, since the model of the bit count versus the quantization parameter relation, parameterized by macroblock variance, is a discrete model generated solely from measurements, We extend their technique for low-delay video rate control (tight buffer regulation) in two ways. We propose a strategy of near-uniform quantization parameter assignments to the macroblocks of a frame that can come close to maximizing an objective spatial quality function, such as PSNR, over the entire frame. We also adaptively update the quantization parameter assignments for the yet to be coded macroblocks, after the encoding of each macroblock, to compensate for any errors in the bit count estimation of the encoded macroblock. Our experiments demonstrate that the proposed rate control method can more accurately control the number of bits expended for a frame, as well as yield a higher objective spatial quality than the method adopted by TMN8.Yayın Representation of speech signals by single signature base function within optimum frame length(IEEE, 2000) Akdeniz, Rafet; Yarman, Bekir Sıddık BinboğaBefore this study, we proposed a novel method to represent signals in terms of, so called, “Signature Base Functions-SBF" which were extracted from the physical features of the waveform under consideration. SBF were determined in ad-hoc manner, which requires tedious search process, and they were not orthogonal. Furthermore, optimality of SBF was in question. In this work however, we suggest a well-organized procedure to generate “Optimum Orthogonal Signature Base Functions-OSBF" for selected waveforms, which in turn provides excellent means for signal representations. It is shown that the new method of signal representation, which is based on OSBF, requires less computation time with substantial signal compression and results in efficient speaker dependent recognition.Yayın Hızlı sönümlemeli kanallarda yeni bir uzay-zaman-frekans kodlamalı OFDM sistem tasarımı(IEEE, 2004) Oğuz, Onur; Aygölü, Hasan Ümit; Panayırcı, ErdalBu çalışmada, frekans seçici hızlı sönümlemeli kanallarda telsiz iletişim için bir uzay-zaman-frekans çeşitlemesi yöntemi önerilmiştir. Önerilen yöntem, OFDM tekniğini kullanarak frekans seçici kanalı uygun hale getirdikten sonra sırasıyla dik uzay-frekans ve dik uzay-zaman blok kodlama uygulayarak uzay-zaman-frekans çeşitlemesi sağlamaktadır. Elde edilen sistemin başarımını arttırmak üzere sisteme uygun bu kafes kodlama tekniği araştırılmış ve uygun kafes yapısının oluşturulması için yeni kriterler ortaya çıkarılmıştır. Oluşan sistemin başarımını, bilgisayar benzetimleriyle incelenmiş ve var olan yöntemlerle karşılaştırılmıştır.Yayın Analysis of self noise in a clock recovery systems with a high-order nonlinearity(IEEE, 1998) Panayırcı, ErdalThis paper presents a new technique to compute efficiently the I and Q spectra, and the I - Q cross-spectrum of the self noise appearing at the output of the zero-memory, high order nonlinear device employed in a clock recovery system. It is known that these spectra play an important role in the phase jitter performance of the clock regenerator. The results are very general and applicable to many cases of practical interest. A numerical example provided at the end of the paper shows that the new approach yields very accurate results and is much faster that the usual computer simulation method.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 Immitance data modelling via linear interpolation techniques: a classical circuit theory approach(Wiley-Blackwell, 2004-11) Yarman, Bekir Sıddık Binboğa; Kılınç, Ali; Aksen, AhmetWith the advancement of the manufacturing technologies to produce new generation analog/digital communication systems, immitance data modelling has gained renewed importance in the literature. Specifically, models are utilized for behaviour characterization, simulation of physical devices or to design sub-systems with active and passive solid-state devices. Therefore, in this paper, new computer aided tools are presented to model one port immitance data by means of linear interpolation techniques. The basic philosophy of the new modelling tools is based on the numerical decomposition of the immitance data into its minimum and Foster parts. Computer algorithms are presented to model the minimum and the Foster parts of the given immitance data. Implementations of these algorithms are exhibited by means of examples. Depending on the application, modelling tools based on linear interpolation techniques may present 'computational and practical' advantages over the existing interpolation techniques, non-linear curve fittings or regression methods. It is expected that the new modelling tools will be utilized to provide initial circuit topologies to the commercially available analysis/simulation and design packages.Yayın Circuit model for given reflectance data constructed with mixed lumped and distributed elements for high speed/high frequency communication systems(IEEE, 2005) Yarman, Bekir Sıddık Binboğa; Şengül, Metin; Kılınç, Ali; Aksen, AhmetIn this paper, a reflectance-based "non linear interpolation method" is presented to model the measured or computed data, obtained from a "passive one-port physical device" using mixed lumped and distributed elements. Mixed element model is constructed with cascade connection of series inductors [L], commensurate transmission lines or so called Unit Elements [UE] and shunt capacitors[C]. Basis of the new model rests on the numerical generation of the scattering parameters of the lossless two-port constructed with cascade connection of simple [L]-[UE]-[C] elements which describes a lossless 2-port in Darlington sense. The new modeling technique does not require direct optimization of the circuit elements of the selected topology. Rather, two-variable reflection coefficient is directly determined by means of a non linear but "convergence guaranteed" interpolation process to best fit the given data. A low-pass filter input reflection coefficient modeling example is included to exhibit the utilization of the proposed modeling method.Yayın Linear expansions for frequency selective channels in OFDM(Elsevier GMBH, 2006) Şenol, Habib; Çırpan, Hakan Ali; Panayırcı, ErdalModeling the frequency selective fading channels as random processes, we employ a linear expansion based on the Karhumen-Loeve (KL) series representation involving a complete set of orthogonal deterministic vectors with a corresponding uncorrelated random coefficients. Focusing on OFDM transmissions through frequency selective fading, this paper pursues a computationally efficient, pilot-aided linear minimum mean square error (MMSE) uncorrelated KL series expansion coefficients estimation algorithm. Based on such an expansion, no matrix inversion is required in the proposed MMSE estimator. Moreover, truncation in the linear expansion of channel is achieved by exploiting the optimal truncation property of the KL expansion resulting in a smaller computational load on the estimation algorithm. The performance of the proposed approach is studied through analytical and experimental results. We first exploit the performance of the MMSE channel estimator based on the evaluation of minimum Bayesian MSE. We also provide performance analysis results studying the influence of the effect of SNR and correlation mismatch on the estimator performance. Simulation results confirm our theoretical results and illustrate that the proposed algorithm is capable of tracking fast fading and improving performance.Yayın A parametric approach to construct two-variable positive real impedance functions for the real frequency design of mixed lumped-distributed matching networks(IEEE, 2004) Aksen, Ahmet; Pınarbaşı, Hacı; Yarman, Bekir Sıddık BinboğaIn this paper, a parametric approach to construct two-variable positive real driving point impedance functions characterizing lossless ladder networks with mixed lumped and distributed elements is presented. The proposed approach is based on the generation of two-variable positive real impedance functions from the single variable boundary conditions. Utilizing the proposed parametric construction algorithm, real frequency matching technique is extended to the design of matching networks with mixed lumped and distributed elements. The application of the approach is illustrated by a broadband microwave amplifier design incorporating mixed lumped and distributed type matching networks. The resultant design has been compared with the AWR Microwave Office software simulation.
