List of Articles
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Open Access Article
1 - Better performance of special triangular constellations for the OFDM systems in complicated fading channel
saeed ghazi-maghrebiDue to high spectral efficiency, immunity to frequency selective fading, and high data rate, OFDM became a popular modulation technique in digital communication systems. Effectiveness of a signal constellation used in a communication system can provide a fundamental bas MoreDue to high spectral efficiency, immunity to frequency selective fading, and high data rate, OFDM became a popular modulation technique in digital communication systems. Effectiveness of a signal constellation used in a communication system can provide a fundamental basis for efficiency of application networks. During recent years, different constellations were designed for different modulation schemes. In this research, two new triangular constellations schemes which are named as TRI1 and TRI2 are introduced to replace for the well-known rectangular QAM constellation in OFDM modulation. In this paper, the new proposed schemes are compared with different triangular constellations. It has been shown that these new schemes have three major advantages with respect to the QAM. The first advantage is its lower BER which results from the better usage of the constellation space with longer minimum distances. The second advantage of these schemes is their lower PAR with respect to the rectangular QAM constellation. The third property, as the last advantages, is their higher noise immunity with respect to the commonly used QAM constellation. Both mathematical analysis and simulation results demonstrate that by applying high fading channels with AWGN and ISI impairment simultaneously, the TRI1 and TRI2 exhibit a superior performance compared to the rectangular QAM. As a result, they are good choice for high speed and real-time multicarrier applications such as DAB, DVB, and WiFi at no extra cost. Manuscript profile -
Open Access Article
2 - Analysis of expert finding algorithms in social network in order to rank the top algorithms
AhmadAgha kardan Behnam BozorgiThe ubiquity of Internet and social networks have turned question and answer communities into an environment suitable for users to ask their questions about anything or to share their knowledge by providing answers to other users’ questions. These communities designed f MoreThe ubiquity of Internet and social networks have turned question and answer communities into an environment suitable for users to ask their questions about anything or to share their knowledge by providing answers to other users’ questions. These communities designed for knowledge-sharing aim to improve user knowledge, making it imperative to have a mechanism that can evaluate users’ knowledge level or in other words “to find experts”. There is a need for expert-finding algorithms in social networks or any other knowledge sharing environment like question and answer communities. There are various content analysis and link analysis methods for expert-finding in social networks. This paper aims to challenge four algorithms by applying them to our dataset and analyze the results in order to compare the algorithms. The algorithms suitable for expert finding has been found and ranked. Based on the results and tests it is concluded that the Z-score algorithm has a better performance than others. Manuscript profile -
Open Access Article
3 - Design and Implementation of an Ultra-Wide Band, High Precision, and Low Noise Frequency Synthesizer
Yas Hosseini Tehrani Nasser MasoumiThis paper presents system-level design and implementation of an ultra-wide tunable, high precision, fast locking, low phase noise, and low power portable fractional-N frequency synthesizer. The output frequency of the proposed design is ranged from 54 MHz to 6.8GHz. Th MoreThis paper presents system-level design and implementation of an ultra-wide tunable, high precision, fast locking, low phase noise, and low power portable fractional-N frequency synthesizer. The output frequency of the proposed design is ranged from 54 MHz to 6.8GHz. The VCO cores cover frequencies from 3.4GHz to 6.8GHz. The programmable output dividers allow generation of the lower frequencies. The frequency resolution of the implemented system is ±20 parts per million (ppm) over -40/85ºC. The output power is tunable between -4dBm and +5dBm. The implemented system has a phase adjust feature that allows shifting of the output phase in relation to the reference oscillator ranged from 0° to 180°. It can generate a wide range, high precision, and linear frequency sweep. The sweep rate, frequency step, and frequency range are tunable. The new frequency tuning algorithm, named Yas algorithm, is proposed to improve frequency precision of the synthesizer. To demonstrate the efficiency of the Yas algorithm, the simulation result MATLAB and the experimental measurements are presented. The system consumes 300mA; therefore, it can be powered by Li-Ion battery. The output phase noise is -95.55 dBc/Hz at 1KHz offset from 3GHz. The experimental measurement results demonstrate that the implemented frequency synthesizer can be used for applications, such as oscillator of spectrum analyzer, automatic test equipment, FMCW radars, high-performance clock source for high speed data converter Manuscript profile -
Open Access Article
4 - Analysis of Imperfect Space Channel for the Next Generation Satellite Networks
pedram hajipour ali shahzadiAn efficient space data management is imperative in guaranteeing the best performance with a fair distribution of next generation satellite networks. Therefore, one of the major challenges of implementing this kind of future satellite networks is evaluation any untruste MoreAn efficient space data management is imperative in guaranteeing the best performance with a fair distribution of next generation satellite networks. Therefore, one of the major challenges of implementing this kind of future satellite networks is evaluation any untrusted error for the best Quality of Service (QoS). Therefore, Bit Error Rate (BER) criteria based on the type of space channel which it can be defined prefect or imperfect state between satellites and ground stations seems to be a major challenge for space communication. In this paper, the authors provide a bandwidth sharing algorithm for a proposed future satellite networks under multi-beam prototype. This structure has many antennas in transmitter and receiver sides (satellite and ground stations) which they will be communication together based on space data. Using the above framework, the coverage probability and MIMO capacity for a typical multi-beam satellite system is compared with a single antenna for satellite and multi-antenna for area side coverage based on input parameters such as path loss and Signal to Noise Ratio (SNR), respectively. Finally, the bit error rate based on imperfect channel estimation is obtained by employing 4-QAM and QPSK digital modulations and the number of antennas followed by a comparative analysis. Manuscript profile -
Open Access Article
5 - Lifetime Maximization by Dynamic Threshold and Sensor Selection in Multi-channel Cognitive Sensor Network
Asma Bagheri Ataollah Ebrahimzadeh maryam najimiThe tiny and low-cost sensors cannot simultaneously sense more than one channel since they do not have high-speed Analog-to-Digital-Convertors (ADCs) and high-power batteries. It is a critical problem when they are used for multi-channel sensing in cognitive sensor netw MoreThe tiny and low-cost sensors cannot simultaneously sense more than one channel since they do not have high-speed Analog-to-Digital-Convertors (ADCs) and high-power batteries. It is a critical problem when they are used for multi-channel sensing in cognitive sensor networks (CSNs). One solution for this problem is that the sensors sense various channels at different sensing periods. Due to the energy limitation in these scenarios, the lifetime maximization will become an important issue. In this paper, maximizing the lifetime of a CSN is investigated by selecting both the cooperative sensors and their detector threshold, such that the desired detection performance constraints are satisfied. This is a NP-complete problem, and obtaining the optimum solution needs exhaustive search with exponential complexity order. Here we have proposed two convex-based optimization algorithms with low order of complexity. First algorithm applies the known instantaneous Signal-to-Noise-Ratio (SNR) and obtains the proper detector thresholds by solving an equation for every channel. Investigation the effect of detector thresholds on the energy consumption, the false alarm probability and the detection probability shows that we can minimize the detector thresholds such that the detection constraints are met. In the second algorithm in order to reduce the complexity of the problem it is proposed the Bisection method for determining detector thresholds. Because knowing the instantaneous SNR is difficult, we have investigated the performance of the second algorithm by average value of SNR. Simulation results show that the proposed algorithms improve the performance of the network in case of lifetime and energy consumption. Manuscript profile -
Open Access Article
6 - A Global-Local Noise Removal Approach to Remove High Density Impulse Noise
Ali Mohammad Fotouhi Samane Abdoli Vahid KeshavarziImpulse noise removal from images is one of the most important concerns in digital image processing. Noise must be removed in a way that the main and important information of image is kept. Traditionally, the median filter has been the best way to deal with impulse nois MoreImpulse noise removal from images is one of the most important concerns in digital image processing. Noise must be removed in a way that the main and important information of image is kept. Traditionally, the median filter has been the best way to deal with impulse noise; however, the image quality obtained in high noise density is not desirable. The aim of this paper is to propose an algorithm in order to improve the performance of adaptive median filter to remove high density impulse noise from digital images. The proposed method consists of two main stages of noise detection and noise removal. In the first stage, noise detection includes two global and local phases and in the second stage, noise removal is also done based on a two-phase algorithm. Global noise detection is done by a pixel classification approach in each block of the image and local noise detection is performed by automatically determining two threshold values in each block. In the noise removal stage only noisy pixels detected from the first stage of the algorithm are processed by estimating noise density and applying adaptive median filter on noise-free pixels in the neighborhood. Comparing experimental results obtained on standard images with other proposed methods proves the success of the proposed algorithm. Manuscript profile -
Open Access Article
7 - Representing a Model to Measure Absorbency Of Information Technology in Small And Medium Sized Enterprises
Mohammad Taghi Sadeghi Farzad Movahedi Sobhani Ali Rajabzade GhatariWith rapid development of information technology (IT) and further deepening of informationization construction, more and more enterprises have realized the strategic value of IT and made great investments in it. However, during the IT implementation process, decision-ma MoreWith rapid development of information technology (IT) and further deepening of informationization construction, more and more enterprises have realized the strategic value of IT and made great investments in it. However, during the IT implementation process, decision-making, adaptation degree, and IT performance are often inferior to the anticipation. The assimilation of technology can be defined by the extent to which the use of Information technology spreads across organizational processes and becomes routinized in activities. Capabilities of information technology play crucial role in an ever-changing environment and are considered as one of the most important sources for enterprises while enterprises should acquire some effective capabilities so that they can effectively deploy and utilize information technology. The purpose of this investigation is to represent a model to measure absorbency of information technology in small and medium-sized enterprises. To do so, dimensions of the "absorbency of information technology" was determined through exploratory factor analysis in a survey research and confirmatory factor analysis was used to confirm model validity. Findings show that three dimensions are related to absorbency of information technology including the capability for innovative technology, Inside-Out IT capability and IT management capability, among which the capability for innovative technology has the highest correlation with the concept of absorbency of information technology. Manuscript profile -
Open Access Article
8 - ANFIS Modeling to Forecast Maintenance Cost of Associative Information Technology Services
Reza Ehtesham Rasi Leila MoradiAdaptive Neuro Fuzzy Inference System (ANFIS) was developed for quantifying Information Technology (IT) Generated Services perceptible by business users. In addition to forecasting, IT cost related to system maintenance can help managers for future and constructive deci MoreAdaptive Neuro Fuzzy Inference System (ANFIS) was developed for quantifying Information Technology (IT) Generated Services perceptible by business users. In addition to forecasting, IT cost related to system maintenance can help managers for future and constructive decision. This model has been applied by previous large volume of data from IT cost factors, generated services, and associative cost for building pattern, tuning and training this model well. First of all, the model was fully developed, stabilized, and passed through intensive training with large volume of data collected in an organization. It can be possible to feed a specific time period of data into the model to determine the quantity of services and their related maintenance cost. ANFIS forecasting maintenance cost of measured service availability totally provided with first quantifying services in a specific time period. Having an operational mechanism for measuring and quantifying information technology services tangible by users for estimating their costs is contributed to practical accurate investment. Some components have been considered and measured in the field of system maintenance. The main objective of this study was identifying and determining the amount of investment for maintenance of entire generated services by consideration of their relations to tangible cost factors and also intangible cost connected to service lost. Manuscript profile