Background and Objectives: Reliable data transmission and congestion control are considered as the transport layer primary functions in Wireless Sensor Networks (WSNs). WSNs are a specific category of wireless ad-hoc networks where their performance is highly affected by their characteristics and limitations. These limitations necessitate an effective data transport control in WSNs which considers quality of service (QoS), energy efficiency, and congestion control.Methods: Congestion affects normal data transmission and ends in packet loss. Furthermore, wireless channels introduce packet loss because of high bit-error rate which wastes energy and affects reliability. The major problems regarding transport protocols in WSNs are congestion and reliability where the latter is classified and reviewed in the current paper.Results: In this paper, reliable data transport protocols are classified as the traffic direction, the parameter the reliability focuses on, and loss detection, notification, and recovery. Traffic direction-based reliable data transport protocols can be upstream, downstream or bidirectional, however, the parameter-based ones can be packet-based, event-based or destination-based, the loss detection and notification-based ones can be ACK-based, NACK-based, ACK and NACK-based or SACK-based, and the loss recovery-based reliable data transport protocols can be E-2-E or H-by-H. Thereafter, a comprehensive review of different reliable data transport protocols in wireless sensor networks is presented. Also, different performance metrics are used to compare these schemes.Conclusion: In this paper, reliable data transport protocols in WSNs are classified, reviewed and compared using different performance metrics. Finally, the current work attempts to provide specific directives to design and develop novel reliable data transport protocols in wireless sensor networks.
Background and Objectives: In order to compensate the nonlinearity, several linearization approaches such as feedback, feed-forward, and predistortion have been proposed. Among these linearization methods, the analog predistortion (APD) method is very suitable for the power amplifier and TWTA linearization, because it has a good compromise between complexity, linearity improvement and bandwidth. On the other hand, analog predistortion circuit can be added to existing amplifiers as a separate circuit. Many of the reported linearizer circuits are capable of linearizing power amplifiers with high gain and phase variations. However, these circuits are complex and bulky due to the use of distortion producer, phase shifter, adjustable attenuator, combiner/divider, and control unit. The objective of this paper is increasing the dynamic range of the predistorter by a simple proposed circuit. Hence, linearization capability of the linearizer is boosted.Methods: A new analog predistortion linearizer based on a coupler and a Schottky diode is presented. The proposed structure satisfies linearization requirements of the solid-state power amplifiers (SSPAs) and traveling wave tube amplifiers (TWTAs). Using a parallel combination of two Schottky diodes along with transmission line in port 2 and 3 of the coupler, the dynamic range of reflection coefficient of each port is increased compared to using a single diode in each branch. By increasing the range of reflection signal, the linearization capability has been increased to linearize power amplifiers and TWTAs. The AM/AM and AM/PM of the linearizer is controlled by changing the bias voltage of power supply.Results: The simulation results show that about 30° phase shift and 5 dB gain expansion can be compensated for power amplifiers and TWTAs. Because of utilizing two diodes, the linearization capability of the new linearizer is augmented compared to the conventional linearizer.Conclusion: A novel analog predistortion circuit based on the hybrid coupler and Schottky diodes is presented. The suggested topology increases the dynamic range of reflected power from each port. Using the proposed idea, AM/AM and AM/PM characteristics are expanded such that this characteristic can linearize the power amplifier with high linearity.
Background and Objectives: COVID-19 disease still has a devastating effect on society health. The use of X-ray images is one of the most important methods of diagnosing the disease. One of the challenges specialists are faced is no diagnosing in time. Using Deep learning can reduce the diagnostic error of COVID-19 and help specialists in this field. Methods: The aim of this study is to provide a method based on a combination of deep learning(s) in parallel so that it can lead to more accurate results in COVID-19 disease by gathering opinions. In this research, 4 pre-trained (fine-tuned) deep model have been used. The dataset of this study is X-ray images from Github containing 1125 samples in 3 classes include normal, COVID-19 and pneumonia contaminated.Results: In all networks, 70% of the samples were used for training and 30% for testing. To ensure accuracy, the K-fold method was used in the training process. After modeling and comparing the generated models and recording the results, the accuracy of diagnosis of COVID-19 disease showed 84.3% and 87.2% when learners were not combined and experts were combined respectively. Conclusion: The use of machine learning techniques can lead to the early diagnosis of COVID-19 and help physicians to accelerate the healing process. This study shows that a combination of deep experts leads to improved diagnosis accuracy.
Background and Objectives: Applications and systems software that are running constantly become obsolete due to the accumulation of error conditions or the depletion of resources like physical memory or performance degradation. In this regard, software rejuvenation has been proposed to deal with such a phenomenon and prevent software failure in the future. This paper proposes a multiple objective of software rejuvenation models with several policies. The purpose is to identify the right rejuvenation policy in practical situations.Methods: We model software system with four policies using the Markov process. These policies are: (a) Software system without rejuvenation; (b) Software system with partial rejuvenation; (c) Software system with partial and full rejuvenation; and (d) Software system with four different types of rejuvenation. In the models and each policy, we consider assigning the level of performance on which the availability and operating costs are calculated. Results: To evaluate the models with the four policies, many numerical experiments were performed. For each policy, we evaluated and compared three objectives, namely performance, availability and operating costs. The experimental results states that for Software System with the policy of four different type of rejuvenation has about 18 and 16 percent improvement in performance and availability, respectively, compared with those other policies. Moreover, the operating cost of the software system with partial rejuvenation policy is lower and more efficient than other policies.Conclusion: According to the calculated objectives and the results of the policies, it can be concluded that in systems with lower operational costs, the most appropriate policy is the software system with four different types of rejuvenation because this policy bring the maximum possible value for the performance and availability.
Background and Objectives: The principal aim of this paper is to show an independent vector control of two five-phase Linear Induction Motors (LIMs) that are supplied from a single VSI. Methods: The LIMs are running at the same speed but with different load conditions. This concept can be especially beneficial in long trains with distributed power. To achieve excellent control characteristics and to reduce the undesirable tension forces between the train mechanical couplers, Fuzzy Logic Controllers (FLCs) have been utilized.Results: As a result, the fault occurrence of the train control systems decreases, and the system reliability increases. The results prove the electrical independence in control of a five-phase two-LIM drive supplied with a single VSI. Furthermore, in the presence of the train mechanical couplers and connections, the application of FLC offers excellent control characteristics and reduces the undesirable tension forces. Furthermore, to obtain a more worthwhile validation of the theoretical results, an experimental set up has been constructed and results have also been presented.Conclusion: According to the results, the undesirable tension forces imposed on train couplers are reduced. Consequently, it leads to higher system efficiency, lower deterioration of the train couplers and connections, greater system reliability, and higher passenger safety and comfort.
