Earticle

In this paper we provide cross-layer analysis of the impact of mobility and Medium Access Control parameters in IEEE 802.11 wireless network on TCP. Performances of the Internet transport protocols may significantly degrade when end to end connection includes wireless links where packets delays and losses are caused by mobility and transmission errors. We perform analysis of the achievable throughput for different TCP versions, including TCP Tahoe, TCP Reno, TCP New Reno, TCP Vegas and TCP SACK, in IEEE 802.11 wireless networks. The analysis showed that the impact of Medium Access Control parameters, such as number of retransmissions and interface queue length in 802.11 networks on the obtained throughput, is stronger for terminals with higher mobility. Also, the analysis contributed to detection of the most appropriate TCP protocols for different mobility of the users in IEEE 802.11 networks.

The cyber attacks using web sites for a personal information sale or break down the infrastructures are increasing. To prevent cyber attacks, virtual computer systems are hired and dynamic malicious web site analysis systems are used. However the dynamic analysis systems have to setting up a targeted environment and have a threat of real attack. Unlikely the dynamic analysis system, a static malicious web site analysis system can download a web page source and analysis the web page. The static analysis algorism also has problem, the analysis time is longer than dynamic systems and need a human checking. For this reason, this journal suggest new analysis system reducing the dynamic and static system's problems using suspicious malicious web site detection with strength analysis of a JavaScript obfuscation for new hybrid analysis system.

The device efficiency of a silicon SDR (p+nn+) IMPATT diode at Ka-band has been studied by using small signal simulation and field swing upto 50 % of the maximum dc electric field. It is found that the d.c. to r.f. conversion efficiency of the SDR IMPATT diode decreases with the increase in field swing upto 50 %, from 8.98% to 7.84%. An integrated heat sink cum resonant cap cavity has been used for Ka-band oscillator in the present simulation. RF measurements have been performed on a silicon Ka-band SDR (p+nn+) IMPATT diode embedded in the cavity. Simultaneous electronic and mechanical tuning of the oscillator has been carried out to optimize the frequency and generated r.f. power output over the operating range of input d.c. bias current. An optimized r.f. power output of 180 mW has been obtained from the oscillator with an input d.c. bias current 190 mA. The measured output power has been co-related with theoretical estimated r.f. power obtained from simulation from which the efficiency of the resonant cap oscillator has been obtained.

Orthogonal Frequency-Division Multiple Access (OFDMA) is a multi-user version of the Orthogonal frequency-division multiplexing (OFDM). OFDMA is used in the mobility mode of IEEE 802.16 WirelessMAN Air Interface standard, commonly referred to as WiMAX. Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users [1], [2]. The performance of these systems depend on the orthogonality between the transmitted subcarriers alloted to different users. The important advantages of OFDMA are that it enables orthogonality in the uplink by synchronizing users in time and frequency and multipath mitigation without using equalizers and training sequences. However, the orthogonality between codes is often disturbed by the carrier frequency offset due to the Doppler effect in fading channels, time delay due to multipath components and poor synchronization at the receiver.

The central idea of this paper is to propose an innovative watermarking scheme for digital image authentication which embeds watermark into the host image and provides qualities such as imperceptibility, robustness and security. A watermark signal is constructed from feature of original image instead of using external watermark. Several pixels are randomly selected from original image, so that all of them have a valid 3x3 neighborhoods. A binary sequence is constructed from those pixels by comparing them against average values of neighborhoods. The binary sequence is then converted into a watermark pattern in the form of a Hankel matrix to improve security of watermarking process and is then embedded within the host image. The operation of embedding and extraction of watermark is done in high frequency domain of Discrete Wavelet Transform since small modifications in this domain are not perceived by human eyes. This watermarking scheme deals with the extraction of the watermark information in the absence of original image, hence the blind scheme was obtained. The proposed algorithm was verified under common image processing attacks such as salt & pepper noise, Gaussian noise, median filtering, linear filtering, JPEG compression, blurring, scaling, intensity adjustment and histogram equalization. Peak Signal to Noise Ratio (PSNR) and Similarity Ratio (SR) are computed to measure imperceptibility and robustness of the watermark respectively.