No. 4 (2017)
Published:
2017-12-30
ARTICLES FROM THIS ISSUE
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An Improved Downlink MC-CDMA System for Efficient Image Transmission
Abstract
Image compression is an essential stage of the data archiving and transmitting process, as it reduces the number of bits and the time required to complete the transmission. In this article, a study of image transmission over the Multi-Carrier Code Division Multiple Access (MC-CDMA) downlink system is presented. The solution proposed relies on source coding combined with channel coding. The Discrete Wavelet Transform (DWT) method is used in conjunction with the SPIHT coder to compress the image, then the data generated is transmitted with the MC-CDMA technique over a noisy channel. The results show that image transmissions performed over MC-CDMA using the SPIHT model are better than the traditional approach like MC-CDMA in the AWGN channel.
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QoS-based Joint User Selection and Scheduling for MU-MIMO WLANs
Abstract
The shift in Multi-User Multiple Input Multiple Output (MU-MIMO) has gained attention due to its wide support in very high throughput Wireless Local Area Networks (WLANs) such as the 802.11ac. However, the full advantage of MU-MIMO can be utilized only with proper user selection and scheduling. Also, providing Quality of Service (QoS) support is a major challenge for these wireless networks. Generally, user scheduling is done with the acquisition of Channel State Information (CSI) from all the users. In MU-MIMO based WLANs, the number of CSI request increases with the number of users. This results in an increased CSI overhead and in degradation of the overall throughput. Most of the proposals in the literature have not addressed the contention in the CSI feedback clearly. Hence, in this paper a Joint User Selection and Scheduling (JUSS) scheme is discussed and its performance is evaluated in terms of throughput, delay, packet loss and fairness. In the performance comparison some wellknown Medium Access Control (MAC) protocols are considered. The proposed scheme not only enhances throughput, but also avoids contention during CSI feedback period.
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Synthesis and Failure Correction of Flattop and Cosecant Squared Beam Patterns in Linear Antenna Arrays
Abstract
This paper deals with the synthesis of flattop and cosecant squared beam patterns using the firefly algorithm which is based on metaheuristics. This synthesis is followed by the correction of the radiation patterns when unfortunate malfunctioning of the individual elements in the array occurs. The necessary attention is given to the recovery process, with due emphasis on reduction of side lobe level, ripple and the reflection coefficient. Simulation in Matlab shows a successful employment of the firefly algorithm in producing voltage excitations of the good elements necessary for the recovered patterns. The performance of the firefly algorithm in failure correction is validated by duly comparing it with a standard benchmark.
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The Alive-in-Range Medium Access Control Protocol to Optimize Queue Performance in Underwater Wireless Sensor Networks
Abstract
Time synchronization between sensor nodes to reduce the end-to-end delay for critical and real time data monitoring can be achieved by cautiously monitoring the mobility of the mobile sink node in underwater wireless sensor networks. The Alive-in-Range Medium Access Control (ARMAC) protocol monitors the delay of sensitive, critical and real-time data. The idea evolves as it involves reduction in duty cycle, precise time scheduling of active/sleep cycles of the sensors, monitoring the mobility of the sink node with the selection of appropriate queues and schedulers. The model for the path loss due to attenuation of electromagnetic wave propagation in the sea water is explained. The three-path reflection model evaluating reflection loss from the air-water and watersand interfaces as a function of distance between sensors and water depth is introduced. The algorithms for effective path determination and optimum throughput path determination are elaborated. The results verify that implementation of the Alive-in-Range MAC protocol has reduced the total number of packets dropped, the average queue length, the longest time in queue, the peak queue length and the average time in queue significantly, making it relevant for critical and real-time data monitoring.
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Availability Analysis of Different PON Models
Abstract
Due to the increasing demands of individual users, Passive Optical Networks (PON) are a promising technology for future broadband access networks. Reliable access to network services is a very important feature, so the availability of the connection is becoming one of the most important requirements. Failure of the optical fiber occurring between the Optical Line Terminal (OLT) and the passive optical splitter can cause the services becoming unavailable for a large number of users, so it is necessary to prevent such an occurrence by providing backup resources – in this case a spare optical fiber. When constructing the spare path (protection fiber), it is important to keep in mind that, if possible, the working and the spare fiber should not be positioned within the same cable. Failure of the optical fiber between the passive splitter and the individual user also means a loss of service for that user. In that case, protection may be offered by adding spare fibers. The question is, however, whether such a solution is cost-effective, as it would lead to a significant cost increase in the construction of the access network. This paper presents the availability analysis conducted for different PON models.
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Relay-assisted WDM-FSO System: A Better Solution for Communication under Rain and Haze Weather Conditions
Abstract
Among various conventional wireless communication systems, Free Space Optics (FSO) may be distinguished as well, which provides a good level security, high data rates, an enormous bandwidth and negligible susceptibility to electromagnetic interference. The main problem arises with unfavorable weather conditions, which affect the system’s parameters and require an aversion to other paths. The weather conditions discussed are rain and haze. Elimination of their adverse effects is essential for establishing a better communication system. The routing path is a major issue, as its decreased parameters lead to the diversion of the transmitted signal or to its total loss. In this article, increased system path length and proficiency levels are demonstrated by using relays, which are assisted by Wavelength Division Multiplexing (WDM).
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Mobile Cloud for Parallel and Distributed Green Computing
Abstract
Mobile Computing and Mobile Cloud Computing are the areas where intensive research is observed. The “mobility” landscape (devices, technologies, apps, etc.) evolves so fast that definitions and taxonomies do not catch up with so dynamic changes and there is still an ambiguity in definitions and common understanding of basic ideas and models. This research focuses on Mobile Cloud understood as parallel and distributed system consisting of a collection of interconnected (and virtualized) mobile devices dynamically provisioned and presented as one unified computing resource. This paper focuses on the mobile green computing cloud applied for parallel and distributed computations and consisting of outdated, abandoned or no longer needed smartphones being able to set up a powerful computing cluster. Besides showing the general idea and background, an actual computing cluster is constructed and its scalability and efficiency is checked versus the results obtained from the virtualized set of smartphones. All the experiments are performed using a dedicated software framework constructed in order to leverage the nolonger-needed smartphones, creating a computing cloud.
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Monte Carlo Tree Search Algorithm for the Euclidean Steiner Tree Problem
Abstract
This study is concerned with a novel Monte Carlo Tree Search algorithm for the problem of minimal Euclidean Steiner tree on a plane. Given p p p points (terminals) on a plane, the goal is to find a connection between all the points, so that the total sum of the lengths of edges is as low as possible, while an addition of extra points (Steiner points) is allowed. Finding the minimum Steiner tree is known to be np-hard. While exact algorithms exist for this problem in 2D, their efficiency decreases when the number of terminals grows. A novel algorithm based on Upper Confidence Bound for Trees is proposed. It is adapted to the specific characteristics of Steiner trees. A simple heuristic for fast generation of feasible solutions based on Fermat points is proposed together with a correction procedure. By combing Monte Carlo Tree Search and the proposed heuristics, the proposed algorithm is shown to work better than both the greedy heuristic and pure Monte Carlo simulations. Results of numerical experiments for randomly generated and benchmark library problems (from OR-Lib) are presented and discussed.
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Dynamically-adaptive Weight in Batch Back Propagation Algorithm via Dynamic Training Rate for Speedup and Accuracy Training
Abstract
The main problem of batch back propagation (BBP) algorithm is slow training and there are several parameters need to be adjusted manually, such as learning rate. In addition, the BBP algorithm suffers from saturation training. The objective of this study is to improve the speed up training of the BBP algorithm and to remove the saturation training. The training rate is the most significant parameter for increasing the efficiency of the BBP. In this study, a new dynamic training rate is created to speed the training of the BBP algorithm. The dynamic batch back propagation (DBBPLR) algorithm is presented, which trains with adynamic training rate. This technique was implemented with a sigmoid function. Several data sets were used as benchmarks for testing the effects of the created dynamic training rate that we created. All the experiments were performed on Matlab. From the experimental results, the DBBPLR algorithm provides superior performance in terms of training, faster training with higher accuracy compared to the BBP algorithm and existing works.
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Parallel Mutant Execution Techniques in Mutation Testing Process for Simulink Models
Abstract
Mutation testing – a fault-based technique for software testing – is a computationally expensive approach. One of the powerful methods to improve the performance of mutation without reducing effectiveness is to employ parallel processing, where mutants and tests are executed in parallel. This approach reduces the total time needed to accomplish the mutation analysis. This paper proposes three strategies for parallel execution of mutants on multicore machines using the Parallel Computing Toolbox (PCT) with the Matlab Distributed Computing Server. It aims to demonstrate that the computationally intensive software testing schemes, such as mutation, can be facilitated by using parallel processing. The experiments were carried out on eight different Simulink models. The results represented the efficiency of the proposed approaches in terms of execution time during the testing process.
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Detecting Password File Theft using Predefined Time-Delays between Certain Password Characters
Abstract
This paper presents novel mechanisms that effectively detect password file thefts and at the same time prevent uncovering passwords. The proposed mechanism uses delay between consecutive keystrokes of the password characters. In presented case, a user should not only enter his password correctly during the sign-up process, but also needs to introduce relatively large time gaps between certain password characters. The proposed novel approaches disguise stored passwords by adding a suffix value that helps in detecting password file theft at the first sign-in attempt by an adversary who steals and cracks the hashed password file. Any attempt to login using a real password without adding the time delays in the correct positions may considered as an impersonation attack, i.e. the password file has been stolen and cracked.
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Evolution of Measurement of the Single Piece Mail Transit Time
Abstract
The article presents the evolution of measurement of the transit time of priority mail methodology used for postal services quality assessment from the point of view of home and small business senders based on European postal standards. The paper also considers the possibility of test cost reduction by further changes in the measurements methodology.
