New closed-form expressions for SNR estimates of Nakagami fading channels by the method of moments

Method of moments has been a parameter estimation technique appropriate to calculate signal-to-noise ratio (SNR) estimates in fading channel models in which an optimal technique like maximum likelihood estimation is not mathematically tractable. In this article, the ratio of the second moment squared to the fourth moment of the received signal envelope is considered to calculate an exact expression for the SNR estimate in Nakagami-m fading channel for M-QAM and \(\theta \)-MQAM modulations as well as expressions to evaluate the variance and the mean of the estimate. The paper presents two useful contributions for SNR estimation theory on Nakagami fading. Besides the exact algebraic expression for the estimate for a generalized QAM modulation scheme, its performance is evaluated through a statistical linearization argument.     

Image encryption based on the finite field cosine transform

In this paper, a novel image encryption scheme is proposed. The technique involves two steps, where the finite field cosine transform is recursively applied to blocks of a given image. In the first step, the image blocks to be transformed result from the regular partition of subimages of the original image. The transformed subimages are regrouped and an intermediate image is constructed. In the second step, a secret-key determines the positions of the intermediate image blocks to be transformed. Besides complying with the main properties required by image encryption methods, the proposed scheme provides benefits related to computational complexity and encoding of the ciphered-images.     

Three-dimensional steerable discrete cosine transform with application to 3D image compression

This work introduces the three-dimensional steerable discrete cosine transform (3D-SDCT), which is obtained from the relationship between the discrete cosine transform (DCT) and the graph Fourier transform of a signal on a path graph. One employs the fact that the basis vectors of the 3D-DCT constitute a possible eigenbasis for the Laplacian of the product of such graphs. The proposed transform employs a rotated version of the 3D-DCT basis. We then evaluate the applicability of the 3D-SDCT in the field of 3D medical image compression. We consider the case where we have only one pair of rotation angles per block, rotating all the 3D-DCT basis vectors by the same pair. The obtained results show that the 3D-SDCT can be efficiently used in the referred application scenario and it outperforms the classical 3D-DCT.

     

Hypenol,a New Lignan from Hypenia salzmannii

A new lignan, (?)‐secoisolariciresin‐9‐yl 6‐O‐p‐coumaroyl‐β‐D ‐glucopyranoside ( 1 ), named hypenol, along with eleven known compounds, i.e., hyperin, rosmarinic acid, methyl rosmarinate, a mixture of the triterpenes betulinic acid, ursolic acid, and oleanolic acid, glycosylated β‐sitosterol, a mixture of the flavanones sakuranetin and isosakuranetin, hinokinin, and β‐peltatin A dimethyl ether were isolated from the EtOH extract of the leaves of Hypenia salzmannii (Benth. ) Harley . The structures of the compounds were elucidated based on the analysis of spectral data, including MS, 1D‐ and 2D‐NMR, and comparison with data in the literature.     

An ideal gas approach to classify countries using financial indices

Traditionally, countries’ development is classified based on several features that can be related to economic and social factors. However, this classification task is costly due to the difficulty of obtaining those features. We propose a method to classify countries based on financial indices using an ideal gas model. The probability density function (pdf) of the return series of the financial indices is used to characterize the fluctuation of a market. Based on the pdf, the volatility and the B$B$ coefficient, which describe the behavior of world markets, are estimated. The evaluation procedure uses 34 indices from developed and developing countries. The results show that the proposed method is an accurate, fast and low-cost computational alternative to the classifications provided by traditional organizations.     

Bit error probability of the M-QAM scheme subject to multilevel (double) gated additive white Gaussian noise and Nakagami-m fading

Wireless Networks - In this paper, noise models called multilevel gated additive white Gaussian noise (GAWGN) and multilevel double gated additive white Gaussian noise ( $$\hbox...     

New strides towards success

This paper presents a mathematical analysis of the joint effects of additive white Gaussian noise and gated noise in an M-ary Quadrature Amplitude Modulation communication system subject to Nakagami fading. This channel model is suitable to describe scenarios in which the Nakagami channel is affected by noisy signals originated from switching electronic circuits present in industrial environments, for example. Novel and exact analytic expressions for the bit error probability of the system are derived and computer simulations corroborate the analytic results.     

Bit error probability of the M‐QAM scheme under η‐μ fading and impulsive noise in a communication system using spatial diversity

This paper presents a new and exact expression for the bit error probability (BEP) of the square M‐ary quadrature amplitude modulation (M‐QAM) scheme, with the channel under double gated additive white Gaussian noise (G²AWGN) and η‐μ fading in a communication system using the spatial diversity technique. The expression for the BEP is written in terms of the Appell function. The BEP curves are presented under different values of the number of branches of the maximum ratio combining (MRC) receiver, order of the constellation M, and parameters that characterize mathematically the channel, corroborated by simulations performed with Monte Carlo method.