mohammadhassan majidi

With the ever-increasing growth of the Internet and the expansion of imaging tools, digital images are a huge part of the information we work with. This information often contains sensitive data that requires protection. This paper presents a chaotic image encryption method that effectively safeguards the information contained within digital images. The IEPS encryption system is an image encryption scheme based on a Piecewise linear chaotic map (PWLCM) and the SHA-512 hashing function. This design incorporates two operations: permutation and substitution of image pixels. In the permutation stage, the PWLCM map is employed, and the features of the SHA-512 are utilized to substitute the pixels. The experimental results demonstrate that the PWLCM encryption algorithm successfully encrypts the information within the image and exhibits robust performance against various analyses, including the entropy, histogram, key sensitivity criterion, and resistance to differential attacks.

The abundant benefits of Orthogonal Frequency-Division Multiplexing (OFDM) and its high flexibility have resulted in its widespread applications in many telecommunication standards. One important parameter for improving wireless system’s efficiency is the accurate estimation of channel state information (CSI). In the literatures many techniques have been studied in order to estimate the CSI. Nowadays, the techniques based on intelligent algorithms such as genetic algorithm (GA) and particle swarm optimization (PSO) have attracted attention of researchers. With a very low pilot overhead, these techniques are able to estimate the channel frequency response (CFR) properly only using the received signals. Unfortunately each of these techniques suffers a common weakness: they have a slow convergence rate. In this paper, a new intelligent and different method has been presented for channel estimation using gravitational search algorithm (GSA). This method can achieve accurate channel estimation with a moderate computational complexity in comparison with GA and PSO estimators. Furthermore, with higher convergence rate our proposed method is capable of providing the same performance as GA and PSO. For a two-path fast fading channel, simulation results demonstrate the robustness of our proposed scheme according to the bit error rate (BER) and the mean square error (MSE).