Browsing by Subject "Mean square error"
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Item Open Access Cooperative precoding and artificial noise design for security over interference channels(Institute of Electrical and Electronics Engineers Inc., 2015) Özçelikkale, A.; Duman, T. M.We focus on linear precoding strategies as a physical layer technique for providing security in Gaussian interference channels. We consider an artificial noise aided scheme where transmitters may broadcast noise in addition to data in order to confuse eavesdroppers. We formulate the problem of minimizing the total mean-square error at the legitimate receivers while keeping the error values at the eavesdroppers above target levels. This set-up leads to a non-convex problem formulation. Hence, we propose a coordinate block descent technique based on a tight semi-definite relaxation and design linear precoders as well as spatial distribution of the artificial noise. Our results illustrate that artificial noise can provide significant performance gains especially when the secrecy levels required at the eavesdroppers are demanding. © 1994-2012 IEEE.Item Open Access LMS based adaptive prediction for scalable video coding(IEEE, 2006-05) Töreyin, B. Uğur; Trocan, M.; Pesquet-Popescu, B.; Çetin, A. Enis3D video codecs have attracted recently a lot of attention, due to their compression performance comparable with that of state-of-art hybrid codecs and due to their scalability features. In this work, we propose a least mean square (LMS) based adaptive prediction for the temporal prediction step in lifting implementation. This approach improves the overall quality of the coded video, by reducing both the blocking and ghosting artefacts. Experimental results show that the video quality as well as PSNR values are greatly improved with the proposed adaptive method, especially for video sequences with large contrast between the moving objects and the background and for sequences with illumination variations. © 2006 IEEE.Item Open Access Multicore education through simulation(IEEE, 2009-07) Öztürk, ÖzcanThis paper presents the experiences using a commercial full system simulation platform - Simics - in a graduate Chip Multiprocessors class. The Simics platform enables students and researchers to do research on computer architecture, operating systems, and hardware/software cosimulation. It provides the ability to simulate machines that are not physically available. This platform has been used in Chip Multiprocessors course to help graduate and undergraduate students in related areas. This course deals with both hardware and software issues in Chip Multiprocessors, and concludes with a team project at the end of the semester. The simulation-based approach was successful when student feedback and final projects are considered. ©2009 IEE.Item Open Access Nonparametric estimation of hazard functions and their derivatives under truncation model(Kluwer Academic Publishers, 1993) Gürler, Ü.; Wang, J. -L.Nonparametric kernel estimators for hazard functions and their derivatives are considered under the random left truncation model. The estimator is of the form of sum of identically distributed but dependent random variables. Exact and asymptotic expressions for the biases and variances of the estimators are derived. Mean square consistency and local asymptotic normality of the estimators are established. Adaptive local bandwidths are obtained by estimating the optimal bandwidths consistently. © 1993 The Institute of Statistical Mathematics.Item Open Access On the interplay between channel sensing and estimation in cognitive radio systems(IEEE, 2011) Gursoy, M.C.; Gezici, SinanCognitive radio transmissions in the presence of channel uncertainty are considered. In practical scenarios, cognitive secondary users need to perform both channel sensing in order to identify whether the channel is being occupied by the primary users or not, and also channel estimation in order to learn the channel fading coefficients. Generally, errors occur in both channel sensing and estimation, and this leads to a coupling between the two. More specifically, imperfect sensing affects both the structure and the performance of channel estimation schemes. With this motivation, the interactions between channel sensing and estimation are studied in this paper. In particular, different channel estimation schemes including minimum mean-square error (MMSE), linear MMSE, and mismatched MMSE estimations are analyzed, and their dependence on sensing decisions and their performances are investigated. © 2011 IEEE.Item Open Access Optimal and suboptimal receivers for code-multiplexed transmitted-reference ultra-wideband systems(Wiley, 2013) Tutay, M. E.; Gezici, SinanIn this study, optimal and suboptimal receivers are investigated for code-multiplexed transmitted-reference (CM-TR) ultra-wideband systems. First, a single-user scenario is considered, and a CM-TR system is modeled as a generalized noncoherent pulse-position modulated system. Based on that model, the optimal receiver that minimizes the bit error probability is derived. Then, it is shown that the conventional CM-TR receiver converges to the optimal receiver under certain conditions and achieves close-to-optimal performance in practical cases. Next, multi-user systems are considered, and the conventional receiver, blinking receiver, and chip discriminator are investigated. Also, the linear minimum mean-squared error (MMSE) receiver is derived for the downlink of a multi-user CM-TR system. In addition, the maximum likelihood receiver is obtained as a performance benchmark. The practicality and the computational complexity of the receivers are discussed, and their performance is evaluated via simulations. The linear MMSE receiver is observed to provide the best trade-off between performance and complexity/practicality.Item Open Access Optimal image restoration with the fractional Fourier transform(OSA - The Optical Society, 1998-04) Kutay, M. A.; Özaktaş, Haldun M.The classical Wiener filter, which can be implemented in O(N log N) time, is suited best for space-invariant degradation models and space-invariant signal and noise characteristics. For space-varying degradations and nonstationary processes, however, the optimal linear estimate requires O(N2) time for implementation. Optimal filtering in fractional Fourier domains permits reduction of the error compared with ordinary Fourier domain Wiener filtering for certain types of degradation and noise while requiring only O(N log N) implementation time. The amount of reduction in error depends on the signal and noise statistics as well as on the degradation model. The largest improvements are typically obtained for chirplike degradations and noise, but other types of degradation and noise may also benefit substantially from the method (e.g., nonconstant velocity motion blur and degradation by inhomegeneous atmospheric turbulence). In any event, these reductions are achieved at no additional cost. © 1998 Optical Society of America.Item Open Access Source and filter estimation for Throat-Microphone speech enhancement(Institute of Electrical and Electronics Engineers Inc., 2016) Turan, M. A. T.; Erzin, E.In this paper, we propose a new statistical enhancement system for throat microphone recordings through source and filter separation. Throat microphones (TM) are skin-attached piezoelectric sensors that can capture speech sound signals in the form of tissue vibrations. Due to their limited bandwidth, TM recorded speech suffers from intelligibility and naturalness. In this paper, we investigate learning phone-dependent Gaussian mixture model (GMM)-based statistical mappings using parallel recordings of acoustic microphone (AM) and TM for enhancement of the spectral envelope and excitation signals of the TM speech. The proposed mappings address the phone-dependent variability of tissue conduction with TM recordings. While the spectral envelope mapping estimates the line spectral frequency (LSF) representation of AM from TM recordings, the excitation mapping is constructed based on the spectral energy difference (SED) of AM and TM excitation signals. The excitation enhancement is modeled as an estimation of the SED features from the TM signal. The proposed enhancement system is evaluated using both objective and subjective tests. Objective evaluations are performed with the log-spectral distortion (LSD), the wideband perceptual evaluation of speech quality (PESQ) and mean-squared error (MSE) metrics. Subjective evaluations are performed with an A/B comparison test. Experimental results indicate that the proposed phone-dependent mappings exhibit enhancements over phone-independent mappings. Furthermore enhancement of the TM excitation through statistical mappings of the SED features introduces significant objective and subjective performance improvements to the enhancement of TM recordings. ©2015 IEEE.Item Open Access Turbo/katlamalı kodlanmış SFBC/STBC-OFDM sistemlerinde yinelemeli kanal kestirimi(2006-04) Doǧan, H.; Çırpan, H. A.; Panayırcı, ErdalWe consider the design of turbo receiver structures for space-frequency block coded (SFBC/STBC) OFDM systems in unknown frequency selective fading channels. The Turbo receiver structures for SFBC/STBC-OFDM systems under consideration consists of an iterative MAP Expectation/Maximization (EM) channel estimation algorithm, soft MMSE SFBC/STBC decoder and a soft MAP outer-channel-code decoder. MAP-EM employs iterative channel estimation and it improves receiver performance by re-estimating the channel after each decoder iteration. Moreover, the MAP-EM approach considers the channel variations as random processes and applies the Karhunen-Loeve (KL) orthogonal series expansion. The performance of the proposed approaches are studied in terms of mean square error and bit-error rate. Through experimental results, the effect of a pilot spacing on the channel estimator performance and sensitivity of turbo receiver structures on channel estimation error are studied. © 2006 IEEE.Item Open Access Yapısal veri belirsizlikleri altında yarışmacı doğrusal MMSE kestirim(IEEE, 2014-04) Vanlı, N. Denizcan; Sayın, Muhammed Ö.; Kozat, Süleyman S.Bu bildiride, yapısal veri belirsizlikleri altında doğrusal kestirim problemi incelenmektedir. Maliyet fonksiyonu olarak ortalama karesel hata (MSE) düşünülmüştür ve sınırlı belirsizlikler altında gürbüz bir algoritma önerilmiştir. Sunulan yöntem yarışmacı algoritma yapısına sahiptir ve bu yapıya ulaşmak için doğrusal kestiricinin performansı, bilinmeyen veri belirsizliklerine göre ayarlanmış doğrusal enküçük MSE (MMSE) kestiricisinin performansına göreceli olarak tanımlanmıştır.Daha sonra, bu göreceli performans ölçütünü en kötü durumdaki sistem modeline göre enküçülten doğrusal kestirici bulunmuştur. Bu yarışmacı kestiriciyi bulmak için çözülmesi gereken problemin yarı-kesin programlama (SDP) problemi olarak düşünülebileceği gösterilmiştir. Ayrıca, teorik sonuçları izah etmek için sayısal örnekler sunulmuştur.