Mladen Veinović

Estimation of nonstationary AR model using the weighted recursive least square algorithm

A new method of estimating time-varying AR models using weighted recursive least square algorithm with a variable forgetting factor is described. The variable forgetting factor is adapted to a nonstationary signal by a generalized likelihood ratio algorithm through the so-called discrimination function which gives a good measure of nonstationarity. In this way we connect the results from the areas of nonstationary signal estimation and jump detection, and obtain an algorithm which exhibits a good tracking performance together with a high parameter estimation accuracy. The feasibility of the approach is demonstrated with both simulation data and real speech signals.

VirtualMeshLab: Virtual laboratory for teaching Wireless Mesh Network

This paper analyzed WMN routing protocols, modeling, and implementation of software environment for emulation of nodes in WMN network in education area. Use of emulators would enable students and teachers to research performance of the WMN (Wireless Mesh Network) protocol. This concept would contribute to an easier understanding of the WMN protocol related to different algorithms for transfer of routing traffic between nodes.

Local echo canceler with optimal input for true full-duplex speech scrambling system

The purpose of this paper is to focus on the local echo-canceling problem of full-duplex scrambled speech communications over a two-wire telephone network when the scrambling transformation is located between the handset and body of a telephone. Such a design makes possible very efficient protection against electromagnetic compromising emanation, which in turn substantially enhances the overall security of a protected communication. We propose a new adaptive FIR filter algorithm for local echo cancellation in such applications. The proposed algorithm differs from the conventional one by the construction of input signals in an optimal way using the D-optimal experiment design. In this way, at each step, we generate a new sample of the D-optimal pilot sequence for the filter parameter estimation. Consequently, the adaptation of the local echo canceler is defined as an initialization process in the first phase of each protected telephone call. The advantage in using the proposed adaptive FIR echo canceler is demonstrated through simulation results.

Time-varying AR speech analysis using robust RLS algorithm with variable forgetting factor

In this paper a new robust recursive method of estimating the linear prediction (LP) parameters of an auto-regressive (AR) speech signal model using weighted least squares (WLS) with variable forgetting factors (VFFs) is described. The proposed robust recursive least squares (RRLS) differs from the conventional recursive least squares (RLS) by the insertion of a suitable chosen nonlinear transformation of the prediction residuals. The RRLS algorithm takes into account the contaminated Gaussian nature of the excitation for voiced speech. In addition, VFF is adapted to a nonstationary speech signal by a generalized likelihood ratio (MGLR) algorithm, which accounts for the nonstationarity of a speech signal. The proposed method has a good adaptability to the nonstationary parts of a speech signal, and gives low bias and low variance at the stationary signal segments.

Inverted index search in data mining

Data mining has its origins in various disciplines. Two most important data mining disciplines are statistics and machine learning. Data mining is a process of finding new, useful knowledge from data using different techniques. These techniques provide faster and better search for large amounts of data. Inverted index is structure that can be used in data mining process. That is a sorted list of words, with the list of corresponding documents attached to each word. Authors explored inverted index structure for a big corpus of documents. For that purpose, authors created application that use inverted index structure. Application uses open source library named Lucene.

A new way of covert communication by steganography via JPEG images within a Microsoft Word document

In this paper, we analyze steganography as one of the branches in the application of secret and secure communication. Starting with an overview of steganographic methods and techniques of concealing information in various data formats, we then introduce a new system of information transfer within Microsoft Word documents via JPEG images previously processed with a steganographic tool StegApp 1.1.0, developed by the authors. This steganographic tool is based on the transformation of the JPEG image with a domain transformation technique with parameters obtained by the discrete cosine transform. In order to check the level of protection and performance of the StegApp 1.1.0 tool, it is qualitatively compared to the commercial SteganPEG tool, which works and encodes data in JPEG images in a similar way.

Improving protection of PHP source code using cryptology models

Nowadays there is growing issue in protecting PHP scripts from unwanted using, copying and modifications. Existing solutions on source code level are mostly working as obfuscators, are free, and are not providing any serious protection. Solutions that encode opcode are more secure but are commercial and require closed-source proprietary PHP interpreters extension. Additionally, encoded opcode is not compatible with future versions of interpreters which imply rebuying encoders from authors. Finally, if extension source-code is compromised, all script encoded by that solution are compromised too. In this paper we present a novel model for free and open-source PHP script protection solution. Protection level provided by proposed solution is equal to protection level of commercial solutions. Model is based on conclusions from using standard cryptology models for analyzing strengths and weaknesses of existing solutions when scripts protection is seen as secure communication channel in cryptology.

Fuzzy commitment scheme for generation of cryptographic keys based on iris biometrics

This work presents a method based on information-theoretic analysis of iris biometric that aims to extract homogeneous regions of high entropy. Successful extraction of these regions facilitates the development of effective systems for generation of cryptographic keys of lengths up to 400 bits per iris. At the same time, this approach allows for the application of simpler error correction codes with equal false accept rate levels, which reduces the overall complexity of this class of systems.

Comparative analysis of UDP throughput on IPv4 and IPv6 operating systems in IEEE 802.11n wireless networks protected with WPA2 security protocol

This paper explores and quantifies the impact of WPA2 security protocol on network performance of operating systems in IEEE 802.11n wireless networks. Experiments were conducted under laboratory conditions on a wireless network infrastructure. Obtained data analysis throughput in different security scenarios. This paper analyzed the UDP transport flows generated with different packet sizes on IPv4 and IPv6 64-bit operating systems, Windows 7 and Linux Ubuntu 12. The measurement results show that IPv4 systems achieves greater throughput values than IPv6 systems for the same size of UDP packets. The results also show a decrease in throughput value when WPA2 security protocol is used in IEEE 802.11n wireless networks.

System of assessment security for Android operating system

In this paper we performed analysis of the security assessment Android operating system and its security mechanisms. Methodological was performed qualitative assessment of risks affecting the stability of the operating system. The increased level of risk a negative impact on the stability of the operating system as well as the potential violation of data integrity that would have made the system vulnerable and less stable. Based on analysis of the security is proposed solutions to mitigate unwanted risk.