IRAQI JOURNAL OF COMPUTERS, COMMUNICATIONS, CONTROL AND SYSTEMS ENGINEERING

This paper presents performance analysis of Multiple-Input Multiple- Output - Orthogonal Frequency Division Multiplexing Access (MIMO-OFDMA) wireless system using orthogonal space time block code (OSTBC) over Rayleigh fading channel. OSTBC is an efficient code system that achieves the maximum of diversity gain in mobile communication systems and it is very useful in reducing the processing complexity of the wireless communication system. Several MIMO-OFDMA OSTBC models based on different number of antenna constellation (2Tx,2Rx) and (4Tx,2Rx) have been analyzed. The relationship between Bit Error Rate (BER) and Signal to Noise Ratio (SNR) in Rayleigh fading wireless channel has been studied.The simulation results show the effectiveness and accuracy of the MIMO-OFDMA OSTBC system by decreasing BER for low value of SNR compared with the MIMO-OFDMA system.

Internet represents a shared resource wherein users contend for the finite network bandwidth. Contention among independent user demands can result in congestion, which, in turn, leads to long queuing delays, packet losses or both. Congestion control regulates the rate at which traffic sources inject packets into a network to ensure high bandwidth utilization while avoiding network congestion. In the current Internet, there are two mechanisms which deal with congestion; the end-to-end mechanism which is achieved by the Transmission Control Protocol (TCP) and the intermediate nodes algorithms such as Active Queue Management (AQM) in routers. In this paper, a combined model of TCP and AQM (TCP/AQM) is formulated and first simulated without a controller. The results show that it is unable to track the desired queue size. So, to get better tracking performance, an adaptive PID controller based on wavelet network (AWNPID) is used as AQM in the router queue. The non-adaptive PID controller is also demonstrated, and its weakness to the network dynamic changes is compared to the robustness of adaptive controller (AWNPID). The analytical results for linearized TCP/AQM model are presented in MATLAB version 7.0.

The rapid increase of connection-demand to the internet application services and highly traffic network is the main reason behind the need to scale a reliable network. This paper presents the steps of how to make the network reliable by using Redundancy scheme and how to balance traffic load in order to reach optimal network. The implemented network is based on IEEE 802 LAN standard in which the equipment used in the topology is 3745Cisco's routers module and 2960 Ether Switch. Also the Hot Standby Redundancy Protocol (HSRP), Gateway Load Balancing Protocol (GLBP), and Virtual Redundancy Routing Protocol (VRRP) are implemented in this work. Many tests in this work in order to achieve the load balancing of the implemented protocols (test the redundancy scheme) and to test the network performance through CPU utilization, bandwidth consumption by protocols, and measure the convergence time of the implemented protocols in the network. This paper gives a guideline for Internet Service Provider's Network (ISP) in order to avoid loss of information and increase the productivity and revenue. The obtained results show that the GLBP has the best performance in terms of CPU utilization and convergence time, and also in link consumption in comparison with HSRP and VRRP protocols for the same conditions.

The estimation of optical flow is the basic step for many engineering applications that exploit the image processing field as a part of their models. In this paper a model called Slantlet Based Optical Flow Estimation (SLT_OFE) is proposed to estimate the optical flow. Slantlet Transform (SLT) used as an effective tool, 2D and 3D- SLT- Level 2 (SLT2) are computed and employed in the proposed model to provide high accuracy estimation of the optical flow. By its definition, optical flow is a velocity field, so the velocities in this paper are computed using the widely used Differential Technique. Two methods from this technique are adopted; Horn-Schunck Method and Lucas-Kanade Method. The optical flow is estimated for two types of image sequences; synthetic sequences and real sequences. Unlike the real sequences, the synthetic sequences have known true velocities which are used for evaluating the proposed model by calculating mean error (Mean Err.), angular error (Ang. Err.) and Standard Deviation (STD). For extreme study of its performance, the proposed SLT_OFE is compared with three other models that are based on level two (Discrete Wavelet Transform (DWT), Discrete Multi Wavelet Transform (DMWT) and Framelet Transform (FT) ) which are implemented in this paper and employed in the conventional models, 2D-DWT2_OFE, 2D-DMWT2_OFE and 2D-FT2_OFE. The results show that the proposed model offers minimum values in errors and STD when 2D-SLT2 is used, and these results are improved by using 3D-SLT2. This leads to the fact that the proposed model SLT_OFE through both of 2D and 3D approaches possesses an improvement in the optical flow estimation process with higher accuracy, than the other models produced in the same circumstances. MATLAB Version 7.12 (R2011a) is used to implement the proposed model and the conventional models.

IEEE 802.15.4 is a standard designed for low data rate, low power wireless personal area networks (WPANs) intended to provide interconnection of nodes via radio communication. Such nodes have very limited computation, energy, and communication capabilities. In order to extend the lifetime of the nodes, we propose a fuzzy logic controller to adapt a duty cycle of each node by changing superframe order (SO) based upon the network traffic and node's buffer occupation. Simulating the proposed algorithm in Castalia simulator and comparing it with constant duty cycle schemes are carried out in this paper. Simulation results show that the proposed algorithm decreases drop packets in node's buffer, decreases packet latency and increases energy efficiency.

As mobile computing is more and more widespread, mobility support for Internet devices becomes very important. Mobile IPv6 (MIPv6) is a promising technology that handles the mobility management and provides the seamless mobile communications. It is expected that MIPv6, as a standard for mobile communication, will open the Mobile Internet Age. In this paper, we will discuss the basic principles of MIPv6 operation by means of handoff process and tunneling mechanism. We will also show how to simulate a proposed MIPv6 network scenario. This work is based on a specific simulator named OMNET++ which includes simulation packages. Our simulation results include the throughput of each router in the proposed MIPv6 network; it also includes the handoff latency for each mobile node in the proposed MIPv6 network.

The process of hiding is considered to be one of the important security branches which are used to ensure the safe transfer of vital data and its protection against theft or editing. Recently, the need for developed hiding methods have greatly increased as the programming technologies that are capable of detecting hidden data, which are hidden using conventional methods, have undergone a great leap in progress. This paper aims to introduce a novel method of hiding a text inside an executable (.exe) file. This is considered one of the recent, more developed types. The suggested system has been tested on two types of executable files. The first type was written using (C++.exe) whereas the second was written using (VB.exe). The text was hidden using the suggest method (Cover Region and Parity bits) through which the executable file will be segmented into (regions) afterwards, each group of values will be tested alongside the value of the secret message that needs to be hidden. The suggested approach was applied on several texts and the result was that hiding via the executable files of the (VB) types is faster and it occupies less size than the (C++) type.