Yuli Zhao

Image encryption based on three-dimensional bit matrix permutation

Lately, a number of image encryption algorithms that are either based on pixel level or bit level encryption have been proposed. However, not only pixel level permutation, but also bit level permutation has its intrinsic drawbacks. This paper proposes a new cryptosystem to address these drawbacks. Different kinds of permutation algorithms are first comprehensively analyzed and compared. Because, from a bit level perspective, an image can be considered as a natural three-dimensional (3D) bit matrix (width, height, and bit length), a new 3D bit matrix permutation is proposed, in which the Chen system is used to develop a random visiting mechanism to the bit level of the plain-image. By combining aspects of the Chen system with a 3D Cat map in the permutation stage, a new mapping rule is developed to map one random position to another random position (that is, double random position permutation) in the 3D matrix rather than using traditional sequential visiting to the plain-image. Simulations are carried out and the results confirm the security and efficiency of our new cryptosystem. The problems of pixel- or bit-level permutation are analyzed.A 3D bit level permutation is proposed.A random visiting to plain-image is proposed.

Fractal Color Image Coding Based on Isosceles Triangle Segmentation

Based on isosceles triangle segmentation, a new approach of color image compression has been proposed by using correlation among RGB components and fractal image compression algorithm in this paper. The encoding process in this paper is composed of two steps: transforming color image into gray-level image according to correlation among RGB and compressing fractal image based on isosceles triangle segmentation. Compared to the fractal color image compression method based on Jacquin, the approach proposed in this paper has better performance because the use of isosceles triangle segmentation greatly reduced the searching time. Simulation results show that the proposed method can effectively reduce the encoding time and improve compression ratio while remaining the quality of the retrieved image.

SCALE-FREE LUBY TRANSFORM CODES

This paper reports the characteristics and performance of a new type of Luby Transform codes, namely scale-free Luby Transform (SF-LT) codes. In the SF-LT codes, the degree of the encoded symbol follows a modified power-law distribution. Moreover, the complexity and decoding performance of SF-LT codes are compared with LT codes based on robust soliton degree distribution and LT codes based on suboptimal degree distribution. The results show that SF-LT codes outperform other LT codes in terms of the probability of successful decoding over an ideal channel and a binary erasure channel. Moreover, the encoding/decoding complexity for the SF-LT codes is superior.

Improved online fountain codes

Online fountain codes have been proven to require lower overhead and fewer feedbacks than growth codes for successful decoding. In an attempt to improve the intermediate symbol recovery rate, the authors propose sending a number of degree-1 input symbols prior to the build-up phase based on a simple application of probability theory. In addition, during the completion phase, received encoded symbols with three neighbouring white (un-decoded) symbols are retained for decoding and updating the decoding graph later. The performance and characteristics of the proposed improved online fountain codes are compared to those of the original online fountain codes over an erasure channel. Simulation results reveal that the improved online fountain codes outperform the original fountain codes in terms of intermediate symbol recovery rate, average encoded symbols required to be generated by the sender, average feedback transmissions, and encoding/decoding efficiency.

Automatic Software Refactoring via Weighted Clustering in Method-Level Networks

In this study, we describe a system-level multiple refactoring algorithm, which can identify the move method, move field, and extract class refactoring opportunities automatically according to the principle of “high cohesion and low coupling.” The algorithm works by merging and splitting related classes to obtain the optimal functionality distribution from the system-level. Furthermore, we present a weighted clustering algorithm for regrouping the entities in a system based on merged method-level networks. Using a series of preprocessing steps and preconditions, the “bad smells” introduced by cohesion and coupling problems can be removed from both the non-inheritance and inheritance hierarchies without changing the code behaviors. We rank the refactoring suggestions based on the anticipated benefits that they bring to the system. Based on comparisons with related research and assessing the refactoring results using quality metrics and empirical evaluation, we show that the proposed approach performs well in different systems and is beneficial from the perspective of the original developers. Finally, an open source tool is implemented to support the proposed approach.

SSCSMA-based random relay selection scheme for large-scale relay networks

Abstract Effective relay selection is a way to achieve considerable performance gains in cooperative communication. However, in practice, the best relay may not always be selected due to the difficulty in collecting accurate network information when the network scale is very large or when the channel information is time-varying. In this paper, we propose a suboptimal relay selection scheme where the only information available to the source is the destination location. The proposed scheme consists of three phases. During the first phase, the area of relay selection is narrowed down based on the outage probability and target transmission rate. In the second phase, a node within this region is selected using the Successive Slotted Carrier Sense Multiple Access (SSCSMA) protocol. In the third and last phase, data is transmitted from the source via the relay to the destination. We present a detailed analysis of the transmission rate and the outage probability. Simulation results have shown that our method using SSCSMA outperforms Random Access based Blind Relay Selection (RABRS) in terms of transmission rate. The results have also indicated that both the outage probability constraint and the source-destination distance affect the transmission rate.

Analysis of the Dynamic Influence of Social Network Nodes

In recent years, with the development of the social network theories, how to find or mining the most significant node in social network for understanding or controlling the information dissemination has become a hot topic and a series of effective algorithms have been presented. In this paper, a new scheme to measure the dynamic influence of the nodes in a social network is proposed, in which the sum of trust values of the propagation nodes is used. Simulations have been carried out and the results show that our scheme is stable and accurate.

Generation of Luby Transform Codes with Low Redundancy

Given the same number of encoded symbols, a Luby Transform (LT) decoder is more likely to decode successfully when there is little redundancy among the symbols. With the use of a Tanner graph, we describe two kinds of redundancy appearing in LT codes in this paper. We further propose an encoding algorithm called Low Redundancy (LR) algorithm used in the formation of the encoded symbols. The algorithm aims to reduce the redundancy of LT codes and to improve the decoder performance under the same complexity. Simulation results show various LT codes improve in terms of average overhead factor and probability of successful decoding when the codes are encoded using the proposed LR algorithm. Moreover, the encoding complexity remains unchanged.