Volume 10, Issue 3 , September 2016
Abstract
In this paper design of Store and Forward (S and F) communication payload for a Sina-1satellite is presented. The S and F subsystem uses VHF and UHF radio links for receiving and transmitting messages. It provides digital communication facilities between a numbers of satellite radio operators. The main ...
Read More
In this paper design of Store and Forward (S and F) communication payload for a Sina-1satellite is presented. The S and F subsystem uses VHF and UHF radio links for receiving and transmitting messages. It provides digital communication facilities between a numbers of satellite radio operators. The main purpose of the system is to provide the handling of transmitting/receiving of packet type messages via satellite. A message from one ground terminal is stored in memory on the satellite and delivered as the satellite passes over the destination ground terminal. The two ground terminals do not have to see the satellite at the same time, and a single satellite can provide global communications coverage. The main specifications of store and forward subsystem are calculated and presented. Split channel reservation multiple access (SRMA) protocol is used as the multiple access protocol. The effect of different parameters such as the number of users, packet length and visibility time is analyzed. Phase shift keying (PSK) modulation is used for downlink and uplink transmissions. In order to improve the performance of satellite communications link, error correction technique is used in this payload. Link calculation reveals that a packet service of 4.8 kbps can be provided without satellite tracking mechanisms. Finally the structure diagram of the on-board S and F transceiver is presented.
Vahid Moradi; Farbod Razzazi; Alireza Behrad
Volume 10, Issue 3 , September 2016
Abstract
There is a vast range of potential applications for recognition of handwritten Persian / Arabic digits (e.g. banking transactions, business registration forms and postal code recognition to name a few). In this paper, a new method is presented for automatic recognition of joint two-digit Persian numerals. ...
Read More
There is a vast range of potential applications for recognition of handwritten Persian / Arabic digits (e.g. banking transactions, business registration forms and postal code recognition to name a few). In this paper, a new method is presented for automatic recognition of joint two-digit Persian numerals. The proposed method is composed of a combinational structure of Support Vector Machines (SVM) and a Hidden Markov Models (HMM). In this approach, we used SVM and HMM for classification and segmentation goals respectively. Due to the higher performance of SVM in classification with respect to HMM, the main core of recognition is an SVM classifier. In contrast, we used HMM to detect the location of the boundary for two-digit numerals. To evaluate the method, we employed a selection of HADAF Persian isolated characters corpus. We employed a 4 scale Gabor filter bank (24, 12, 6 and 3 scales) in 6 directions (0, 30, 60, 90, 120, 150 degrees) for feature extraction. The results showed the digit recognition rate of about 98.75 percent for the proposed algorithm on Persian two-digit numerals, while the recognition rates were 98.58 and 95.93 for separate SVM and HMM engines on isolated characters respectively.
Hadi Zayyani; Yaser Attar
Volume 10, Issue 3 , September 2016
Abstract
This paper suggests an oracle normalized least-mean-square (NLMS) algorithm and a simple Bayesian detection NLMS impulse noise detection algorithm as an effective adaptive algorithm against impulsive noises. Initially, to have a fast algorithm, an optimization problem is introduced and then an oracle ...
Read More
This paper suggests an oracle normalized least-mean-square (NLMS) algorithm and a simple Bayesian detection NLMS impulse noise detection algorithm as an effective adaptive algorithm against impulsive noises. Initially, to have a fast algorithm, an optimization problem is introduced and then an oracle NLMS algorithm is devised. It has the largest reduction in misalignment error at each iteration with respect to the previous iteration. Oracle NLMS algorithm needs the values of impulse noises and hence is not practical. To have a practical variant of oracle NLMS algorithm, a simple Bayesian impulse noise detection NLMS algorithm is proposed. It is based on a MAP detection criterion and the impulse noise detection rule is proved to be a comparison of the absolute value of the error of the adaptive filter with a threshold and hence is very simple. Also, by assuming the sparsity of the impulse noises, the value of threshold is obtained via a simple statistical estimation. The simulation results in both dispersive and sparse system cases, show the effectiveness of the suggested algorithm in terms of convergence rate and complexity.
Ghasem Sadeghi Bajestani; Ali Sheikhani; Seyed Mohammad Reza Hashemi Golpayegani; Farah Ashrafzadeh; Paria Hebrani
Volume 10, Issue 3 , September 2016
Abstract
Solving many of the scientific problems in physics and engineering leads to differential equations, which in many cases no analytical answers can be found. The question to be considered is that if the available numerical methods for solving diferential equations (that are all done by computers) are reliable. ...
Read More
Solving many of the scientific problems in physics and engineering leads to differential equations, which in many cases no analytical answers can be found. The question to be considered is that if the available numerical methods for solving diferential equations (that are all done by computers) are reliable. Is the Lipschitz validity assumption on differential equations with nonlinear dynamics true? What is the reason for the contradictory outcomes of solving a simple equation using numerical methods? Do the outcomes show the reality of the dynamic system? What is the acceptable replacement for the current methods? All the phenomena of the world have bifurcations, singularity, dissociation, behavioral changes and interaction; and today, science with assumptions like neglecting interactions and singularities, consider the systems as a continues model, although we are in need of a model in which we can solve the problem without inserting the changes in time approach to zero chain. In this article, accompanied by showing different and contradictory results –which are all wrong– numerical methods for solving a simple differential equation and comparing them with analytical method, we introduce Poincare as a substitution for overcoming this scientific derivation. In this article we solved a differential equation with common numerical methods in MATLAB, and showed that these methods produce conflicting outcomes, and then we solved it using Poincare. After showing the invalidity of common numerical methods and introduction of a simple decomposition method, we investigated Van der Pol equations using Poincare, and showed the fact that Poincare can simply show the system dynamics like a flashlight.
Navid Daryasafar; Omid Borazjani
Volume 10, Issue 3 , September 2016
Abstract
In high capacity systems, as the bit transmission rate increases, Inter Symbol Interference (ISI) caused by the multi-path channel reduces the system efficiency. Orthogonal Frequency Division Multiplexing (OFDM) technique acts very well against this phenomenon. Moreover, an accurate estimation of the ...
Read More
In high capacity systems, as the bit transmission rate increases, Inter Symbol Interference (ISI) caused by the multi-path channel reduces the system efficiency. Orthogonal Frequency Division Multiplexing (OFDM) technique acts very well against this phenomenon. Moreover, an accurate estimation of the communication channel coefficients improves the performance of communication systems effectively. In this paper, for Multiple Input Multiple output(MIMO) systems using OFDM technique that is based on the least Squares (LS) algorithm, an improved channel estimation algorithm is presented. Accordingly, investigating the channel estimation method, we can design optimum training courses for these systems based on LS algorithm. Simulation shows the efficiency of suggested LS algorithm. We also provided the results of the communication channel estimation.
Navid Razmjooy; Mehdi Ramezani; Ali Namadchian
Volume 10, Issue 3 , September 2016
Abstract
Flexible manipulators are very commonly used in industries. In this paper a single-link flexible joint robot is modeled firstly by using Euler–Lagrange energy equation. An optimized Linear Quadratic Regulator is employed to control the manipulator. After that, a Linear Quadratic Regulator (LQR) controller ...
Read More
Flexible manipulators are very commonly used in industries. In this paper a single-link flexible joint robot is modeled firstly by using Euler–Lagrange energy equation. An optimized Linear Quadratic Regulator is employed to control the manipulator. After that, a Linear Quadratic Regulator (LQR) controller is used for optimal control of the manipulator. For optimizing the LQR, the regulator term weighting of the LQR is achieved by using the newly introduced grey wolf optimizer technique. With the optimized LQR controller based on the proposed performance index, it is tried to have a system with the minimum overshoot and settling time. By considering the proposed performance index and comparing with the PSO-based controller as a popular algorithm, the superiority of the proposed LQR controller in improving the stability and performance of the manipulator is shown. The simulations are performed in MATLAB environment and the results confirm the efficiency of the proposed controller.
Zahra Razavinasab; Mohammad Ali Vali; Mahmoud Samavat
Volume 10, Issue 3 , September 2016, Pages 1-7
Abstract
For linear time-invariant continuous-time singular systems, two new simple approaches, the Kronecker method and the recursive method, are developed in order to estimate the states from the system input-output information via shifted Legendre polynomials (SLP) and a simple observer in the descriptor form. ...
Read More
For linear time-invariant continuous-time singular systems, two new simple approaches, the Kronecker method and the recursive method, are developed in order to estimate the states from the system input-output information via shifted Legendre polynomials (SLP) and a simple observer in the descriptor form. Sufficient conditions for the existence of the present observer are given. The two methods simplify the system of state equations into the solution of a set of linear algebraic equations. Furthermore, the proposed algorithms can be easily implemented in a digital computer and the solutions can be obtained for any length of time. Further, these approaches include the filtering and the smoothing effect which can reduce the influence of zero-mean measurement noise on estimation. Simulation results of a given numerical example demonstrate the effect of the proposed approaches.
