345 research outputs found
Iterative EM-Based Channel Estimation for STBC-OFDM
No full textIEEE Wireless Communications and Networking Conference, WCNC 2009; Budapest; Hungary; 5 April 2009 through 8 April 2009In this paper, an iterative EM based channel estimation algorithm is studied for STBC-OFDM systems. Compared to the time domain EM based channel estimation algorithm which needs matrix inversion, a frequency domain EM based channel estimation algorithm is proposed by estimating the channel coefficients for each subcarrier. The proposed channel estimation algorithm decreased the complexity without sacrificing the performance. The time domain and proposed frequency domain EM based channel estimation algorithms are compared in terms of bit error rate (BER), mean square error (MSE) and the number of iterations used in the EM algorithm
Distance based selection for user-relaying in OFDMA-based wireless networks
No full text24th Signal Processing and Communication Application Conference, SIU 2016; Zonguldak; Turkey; 16 May 2016 through 19 May 2016Düşük kurulum maliyetine ve geniş kapsama alanına sahip kullanıcı-rölelerle geliştirilmiş dikgen frekans bölmeli çoklu erişim (DFBÇE) tabanlı kablosuz ağlar, yüksek veri hızlarına iletişime olanak sağlamaları açısından gelecek nesil iletişim sistemlerinde önemli bir yer tutmaktadır. Kullanıcı-röleli sistemlerde
kullanıcı sayısına paralel olarak artan röle sayısı performansı arttırmaktadır. Tüm kullanıcıların röle olma durumu performans açısından olumlu bir durum olmasına rağmen sinyalleşme yükünü ve dolayısıyla karmaşıklığı çok arttırdığı için pratik sistemlere uygun olmayabilir. Bu nedenle, bu çalışmada
performans ve sinyalleşme yükü arasındaki ödünleşimi dengelemek için kullanıcı-röle adayları belirli bir alanda uzaklığa dayalı olarak seçilmiş ve sonuçlar benzetimler yapılarak değerlendirilmiştir.OFDMA-based user-relay assisted wireless networks which have lower infrastructure cost and larger coverage areas are important technologies for the next generation communication systems since they allow to communicate at higher data rates. The performance of the system is increased with user-relaying since the number of user-relays scales with the number of mobile users. Although, it is good to assume all mobile users are the user-relay candidates, it is not suitable for the practical systems because of the rising signalling overhead and complexity. Thus, in this study, the user-relay candidates are selected in a limited area based on a distance parameter in order to balance the trade-off between the system performance and the signalling overhead and the results are evaluated by performing simulations
Adaptive limited feedback for intercell interference cancelation in cooperative downlink multicell networks
No full text7th International Symposium on Wireless Communication Systems, ISWCS'10; York; United Kingdom; 19 September 2010 through 22 September 2010In this paper, we evaluate intercell interference cancelation techniques in cooperative downlink multicell systems. We compare two classical beamforming strategies for the design of the beamforming vectors: maximum ratio combining precoding and partial zero-forcing. Since full channel state information at the transmission is unfeasible, we consider a limited feedback link and compare different strategies for bit partitioning of the feedback information for serving and interferer base stations. We propose a simple adaptive bit partitioning strategy to select an optimum transmission scheme at the base station. We show that the adaptive bit portioning algorithm is improved the sum capacity performance of the multicell networks significantly.INTERCELL project contract number PIEF-GA-2009-25512
Resource allocation for user-relay assisted MISO-OFDMA networks
No full text12th International Symposium on Wireless Communication Systems, ISWCS 2015; Brussels; Belgium; 25 August 2015 through 28 August 2015The next generation cellular networks request higher capacity and coverage that user-relay assisted Orthogonal Frequency Division Multiple Access (OFDMA) networks are costeffective solutions to meet these demands. These networks can be enriched with multiple antennas in order to obtain a diversity gain to combat signal fading and to achieve more capacity gain without increasing the bandwidth or transmit power. However, radio resource management (RRM) such as relay selection and resource allocation (RA) is important in such a multi-user, multirelay and multi-antenna environment to fully take advantage of multiple-input single-output (MISO)-OFDMA based user-relay assisted cellular networks. Thus, we propose a RA algorithm for these networks to reveal the benefits of the combination of userrelaying and multiple antennas technologies and compare the proposed scheme with existing schemes in terms of percentage of satisfied users and cell-edge users' data rate
Adaptive bit partitioning strategy for cell-edge users in multi-antenna multicell networks
No full textIEEE 12th International Workshop on Signal Processing Advances in Wireless Communications, SPAWC 2011; San Francisco, CA; United States; 26 June 2011 through 29 June 2011In this paper, we improve the performance of cell-edge users by applying adaptive bit partitioning for intercell interference cancelation in cooperative downlink multicell systems. The strategy for partitioning quantization bits between serving and interfering base stations affects the performance of the cooperative networks which is quite sensitive to the quality of the channel state information. The existing transmission strategies are based on the maximization of average cell rate which results in a reduced rate for the users in the cell-edge regions. We propose an adaptive bit partitioning strategy to improve the rate of cell-edge users at the same average feedback link rate. We show the performance of the cell-edge users is significantly increased while keeping the same average cell rate. © 2011 IEEE.INTERCELL project with the contract number PIEF-GA-2009-25512
Fairness aware resource allocation for downlink MISO-OFDMA systems
No full textIEEE Wireless Communications and Networking Conference, WCNC 2012; Paris; France; 1 April 2012 through 4 April 2012In this paper, a resource allocation problem for downlink multiple input-single output orthogonal frequency division multiple access (MISO-OFDMA) systems is investigated. The problem is defined as maximizing the minimum user rate with the constraints of total power and bit error rate (BER). Since it is difficult to obtain the optimal solution to this problem, a suboptimal but efficient solution is proposed based on zero forcing beamforming (ZFBF) to reduce computational complexity. The proposed algorithm is a fairness aware radio resource allocation algorithm that shares the resources equally among the users who has different distances from the Base Station (BS). The simulation results show that the proposed algorithm satisfies the fairness criterion having higher data rates compared to the existing algorithms. © 2012 IEEE
Adaptive resource allocation for SDMA-OFDMA systems with genetic algorithm
No full text6th International Symposium on Wireless Communication Systems, ISWCS'09; Tuscany; Italy; 7 September 2009 through 10 September 2009In this paper, we propose an adaptive resource allocation algorithm to maximize the sum data rate for spatial division multiplexing access (SDMA) orthogonal division multiple access (OFDMA) systems using genetic algorithm. We perform Zero forcing (ZF) beamforming at the transmitter constructing single and multiple beams for OFDMA systems with multiple transmit antennas. In order to reduce the complexity and convergence time of genetic algorithm (GA), we present an initial condition obtained by allocating the user to the subcarrier with maximum precoding gain. The proposed algorithm reduces the complexity without sacrificing the performance. We obtain the simulation results and compare them with the classical static and adaptive allocation methods. We show that the GA with the proposed initial condition increases the sum data rate compared to classical GA and reduces the convergence time significantly for SDMA-OFDMA systems
A novel semantic smoothing kernel for text classification with class-based weighting
No full textAltınel, Berna (Dogus Author), Diri, Banu (Dogus Author), Ganiz, Murat Can (Dogus Author) -- #articleinpress#Altınel, Berna (Dogus Author), Diri, Banu (Dogus Author), Ganiz, Murat Can (Dogus Author)In this study, we propose a novel methodology to build a semantic smoothing kernel to use with Support Vector Machines (SVM) for text classification. The suggested approach is based on two key concepts; class-based term weighting and changing the orthogonality of vector space. A class-based term weighting methodology is used for transformation of documents from the original space to the feature space. This class-based weighting basically groups terms based on their importance for each class and consequently smooths the representation of documents. This is accomplished by changing the orthogonality of the Vector Space Model (VSM) with introducing class-based dependencies between terms. As a result, on the extreme case, two documents can be seen as similar even if they do not share any terms but their terms are similarly weighted for a particular class. The resulting semantic kernel can directly make use of class information in extracting semantic information between terms, therefore it can be considered as a supervised kernel. For our experimental evaluation, we analyze the performance of the suggested kernel with a large number of experiments on benchmark textual datasets and present results with respect to varying experimental conditions. To the best of our knowledge, this is the first study to use class-based term weighting in order to build a supervised semantic kernel for SVM. We compare our results with kernels that are commonly used in SVM such as linear kernel, polynomial kernel, Radial Basis Function (RBF) kernel and with several corpus-based semantic kernels. According to our experimental results the proposed method favorably improves classification accuracy over linear kernel and several corpus-based semantic kernels in terms of both accuracy and speed
VIBRATIONAL SPECTRA OF THE MLCl COMPLEX FROM THEORETICAL CALCULATIONS
No full textAuthor Institution: Department of Physics, Mustafa Kemal University, Hatay, Turkey, 31034 (email to B.C.: [email protected])The geometric and vibrational parameters (harmonic and anharmonic frequencies) of the MLCl [M= Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg; L= Ethylenediamine (en)] donor-acceptor complexes have been studied by using HF and MPW1PW91+iop(3/76=00572004280)/gen methods. Binding, reorganization, atomization, HOMO-LUMO and ionization potential energies have also been calculated with the same method. SQM calculations have been performed by using anharmonic frequencies and experimental data. The obtained results were found to be in good agreement with the corresponding experimental findings
Space-frequency grouping based key extraction for MIMO-OFDM systems
No full textInternational Symposium on Wireless Communication Systems (ISWCS); AUG 28-31, 2017; Bologna, ItalyLatest developments in wireless communication networks push the limits of conventional security methods. Security can be improved with a secret key that is dynamically generated based on the surrounding physical environment. With this objective, physical layer security approaches can be implemented by means of simple signal processing methods. In this paper, we propose novel key extraction approaches based on spatial and frequency characteristics of the wireless environment. In a 2x2 MIMO-OFDM system, low key disagreement rates and key error rates are observed, proving the potential of physical layer key extraction techniques
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