Journal of Communications and Information Technology
پیاپی 2 (Autumn 2012)

a watermarking scheme for Grayscale image isproposed based on a family of the chaotic maps and discretecosine transform. Jacobian Elliptic mapis employed to encrypt ofwatermarked logo. Piecewise nonlinear chaotic map is also usedto determine the location of DCT coefficients for the watermarkembedding. The purpose of this algorithm is to improve theshortcoming of watermarking such as small key space and lowsecurity. Therefore the size of key space for initial conditions andcontrol parameters is computed about and this keyspace is large enough to resist the attacks. Toevaluate therobustness and effectiveness of proposed method, several attacksare applied to the

Co-channel interference is a major factor in limiting the capacity and link quality in cellular communications. As the co-channel interference is modeled by lognormal distribution, sum of the co-channel interferences of neighboring cells is represented by the sum of lognormal Random Variables (RVs) which has no closed-form expression. Assuming independent, identically distributed (iid) RVs, the sum of lognormal RVs has been approximated by another log-normally distributed RV in the literature. In practice, the co-channel interference RVs have identical standard deviations (SDs) and different means. In this paper, first a new method based on curve fitting is proposed to approximate the sum of two log-normally distributed RV's with identical SDs and different means. Then a recursive method using the surface fitting is developed for approximating the sum of more than two lognormal RVs. Results show that the proposed method can approximate the first and the second moments of the resulting RV very well

Many performance evaluations for IEEE 802.11distributed coordination function (DCF) have been previouslyreported in the literature. Some of them have clearly indicatedthat 802.11 MAC protocol has poor performance in multi-hopwireless ad hoc networks due to exposed and hidden nodeproblems. Although RTS/CTS transmission scheme mitigatesthese phenomena, it has not been successful in thoroughlyomitting these drawbacks. We argue that when eliminatinghidden node effect with a given protocol is not feasible, onemay sometimes earn more throughput by controlling or evenwisely creating this phenomenon. In this paper we propose anovel solution to improve the performance of IEEE 802.11MAC protocol in multi-hop networks through modifying NAVtimer. We may call this method Dynamic NAV (DNAV) sincethe NAV timer operation changes dynamically with the changeof environment variables. Simulation results show that ourapproach noticeably increases the throughput in multi-hopwireless ad-hoc networks.

Here, we propose an add-drop and a channel drop filter based on two-dimensional photonic crystal all circular ring resonators. These structures are made of a square lattice of silicon rods with the refractive index n1=3.464 surrounded by air (with refractive index n2=1). The broadest photonic band gap occurs at the filling ratio of r/a = 0.17. Two linear defect W1 waveguides couple to the ring. Our add-drop and channel drop filters form by the appropriate coupling distance between the ring and waveguide. The dropping efficiency of both filters in their operational window - the C (1.535-1.565μm) and L (1.565-1.625μm) bands of optical telecommunications - is almost %100 and corresponds to a deca-pole degenerated resonant mode. Normalized frequencies (a/λ), in degenerated mode equal to 0.3684 and 0.3645. Resonant modes of the all circular ring resonator with their corresponding degenerated poles and the transmission spectra are calculated using the PWE, and 2D-FDTD methods respectively.

This paper presents an E-ring shaped printed monopole antenna for UWB applications with dual notched bands performance. In order to generate single frequency band notch function, we applied a U-ring shaped monopole antenna, and by inserting a rectangular ring in the centre of it an E-ring shaped radiating patch created and a dual band-notch function can be achieved. The measured bandwidth of the proposed antenna is from 2.75 GHz to 11.43 GHz (110%) for VSWR < 2. The proposed antenna offers two notched bands, covering all the 5.2/5.8GHz of WLAN, 3.5/5.5 GHz of WiMAX and 4-GHz of C bands ranges. Good radiation behavior within the UWB frequency range has been obtained. The antenna has a small dimension of 10 *17 mm2.

There are a lot of researches in the world about attacks on information systems (IS). Although there have been many attempts to classify threats of IS’s especially in Health Information Systems (HIS), it is still necessary for all health organization to identify new threats and their sources which threaten security of health care domain. The main aim of this paper is to present a research agenda of threats to HIS and identify issues and human factors that assist the implementation and adoption of health information security within the developing countries. In doing so, the authors try to provide a cohesive completeness identification of all threats about HIS and highlight the role of human in all of them. More than 70 threats to HIS are identified by using a large number of disparate data sources. Then they are classified in 30 subjects and finally categorized in seven areas whichuser’s activities are the biggest threat at the core of risks to HIS.

Image denoising by block matching and threedimensionaltransform filtering (BM3D) is a two steps state-ofthe-art algorithm that uses the redundancy of similar blocks innoisy image for removing noise. Similar blocks which can havesome overlap are found by a block matching method and groupedto make 3-D blocks for 3-D transform filtering. In this paper wepropose a new block grouping algorithm in the first step ofBM3D that improves the performance of denoising algorithmespecially in heavy noise conditions. In heavy noise conditions,BM3D causes some artifacts in the filtered image. These artifactsare reduced by the proposed block grouping algorithm. In theproposed block grouping method, beside of a similarity measureused for block matching, the amount of overlap between blocks isconsidered. Experimental results show that the proposed blockgrouping method can improve the performance of BM3D interms of both peak signal-to-noise ratio (PSNR) and visualquality.