Sharif Digital Repository

In this article, we investigate the limiting spectral distribution of the sample covariance matrix (SCM) of weighted/windowed complex data. We use recent advances in random matrix theory and describe the distribution of eigenvalues of the doubly correlated Wishart matrices. We obtain an approximation for the spectral distribution of the SCM obtained from windowed data. We also determine a condition on the coefficients of the window, under which the fragmentation of the support of noise eigenvalues can be avoided, in the noise-only data case. For the commonly used exponential window, we derive an explicit expression for the l.s.d of the noise-only data. In addition, we present a method to... 

Format compliance, a desirable feature of multimedia security systems, means that the secured bitstream resembles the unprotected compressed bitstream. It is called full format compliance, if the scrambled stream can be decoded by a typical decoder. In this paper, we address the issues that are to be carefully taken into account to develop efficient fully format compliant scrambling methods for compressed video. We also propose new selective scrambling methods for securing compressed video streams. The security issues, in different parts of these scrambling methods, are analyzed and their impact on bit-rate and complexity is discussed. We show that our scrambling methods provide... 

Considering the space of constant-weight sequences as the reference set for every optical orthogonal code (OOC) design algorithm, we propose a classification method that preserves the correlation properties of sequences. First, we introduce the circulant matrix representation of optical orthogonal codes and, based on the spectrum of circulant matrices, we define the spectral classification of the set Sn,w of all (0, 1)-sequences with length n, weight w, and the first chip 1. Then, as a method for spectrally classifying the set Sn,w, we discuss an algebraic structure called multiplicative group action. Using the above multiplicative group action, we define an equivalence relation on Sn,w in... 

Semi-Supervised Learning (SSL) has become a topic of recent research that effectively addresses the problem of limited labeled data. Many SSL methods have been developed based on the manifold assumption, among them, the Local and Global Consistency (LGC) is a popular method. The problem with most of these algorithms, and in particular with LGC, is the fact that their naive implementations do not scale well to the size of data. Time and memory limitations are the major problems faced in large-scale problems. In this paper, we provide theoretical bounds on gradient descent, and to overcome the aforementioned problems, a new approximate Newton's method is proposed. Moreover, convergence... 

Lattice Reduction (LR) has been proposed as a method to enhance the performance of MIMO detectors such as ZF, MMSE and V-BLAST. Until recently, the application of LR to the superior K-Best tree-search detection algorithm was not practical due to the significant increase in complexity of K-Best as a result of the distortion of tree symmetry caused by LR. However, in our recently published work we developed an innovative K-Best algorithm to accommodate tree-asymmetry with no additional complexity. In this work, we build on this result and perform a detailed analysis of the effect of various LR algorithms on the performance of LR-aided K-Best. We show that LLL and Seysen provide equivalent... 

Medical images contain human body pictures and used widely in diagnosis and surgical purposes [1]. Compression is needed for medical images for some applications such as profiling patient's data or transmission systems Due to the importance of the information of medical images, lossless or visually lossless compression preferred. Lossless compression mainly consists of transformation and encoding steps. On the other hand, hardware implementation of lossless compression algorithm accelerates real time tasks such as online diagnosis and telemedicine. Lossless JPEG, JPEG-LS and lossless version of JPEG2000 are few well known methods for lossless compression. This paper is focused on the... 

Solvent extraction of molybdenum (VI) and tungsten (VI) by synergism of the mixture of D2EHPA and TBP were conducted in the RDC extractor with perforated structure. The initial aqueous pH, extractant concentration, ammonium hydroxide concentration as a stripping agent, and synergistic enhancement factor were optimized in the initial experiments before collecting column data. In the RDC column, the influence of agitation rate and inlet phase velocities were examined on the hydrodynamic velocities, mass transfer data, and distribution coefficients. The finding data indicated that the impact of agitation speed on the distribution coefficients of molybdenum and tungsten is considerable in...