List of Articles
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Open Access Article
1 - Performance Improvement of Heterogeneous Networks with Backhaul Constraint through Decoupled Uplink and Downlink Access Policy
a. j. Zolfa Zeinalpour-Yazdi Aliakbar tadaion taftOne of the major challenges in the heterogeneous networks, where different base stations with different capabilities serve users, is the access policy for establishing a communication link between the user and its serving node. To overcome this challenge in a heterogene MoreOne of the major challenges in the heterogeneous networks, where different base stations with different capabilities serve users, is the access policy for establishing a communication link between the user and its serving node. To overcome this challenge in a heterogeneous network which also suffers from the backhaul constraint, a special kind of “decoupled uplink and downlink access” policy is proposed in this paper, which let users to be served by different base stations in uplink and downlink communications. More precisely, in order to efficiently utilize the system resources, increase the users’ throughput, and guarantee the users’ fairness, a special load balancing association policy is considered in the uplink transmission and a problem which maximizes the weighted sum of users’ effective rates is solved. Simulation results show that using this association policy for the considered scenario, significantly improves the load balancing index, energy efficiency, and also users’ effective rate compared to the scenario which considers the criterion of the maximum received power of the downlink connection for both uplink and downlink transmissions. In addition we propose an algorithm which further improves the load balancing considering the backhaul constraint of the base stations and evaluate its efficiency. Manuscript profile -
Open Access Article
2 - Analysis and Design of a Low Power Analog to Digital Converter Using Carbon Nano-Tube Field Effect Transistors
Saeedeh Heidari D. DidebanNowadays, analog to digital (A/D) converters are indistinguishable parts of system on chip (soC) structures because they omit the distance between analog real data and digital logic world. Due to this fact and ever increasing trend for using portable instruments, the fi MoreNowadays, analog to digital (A/D) converters are indistinguishable parts of system on chip (soC) structures because they omit the distance between analog real data and digital logic world. Due to this fact and ever increasing trend for using portable instruments, the figures of merit for design of these converters such as speed, power and occupied area are improved. Different methods are proposed to improve the performance of these converters. In this paper, we design a fast and low power ADC using carbon nano-tube field effect transistor (CNTFET) and then its performance is comprehensively compared with a MOSFET based counterpart at the same technology node. The performance is studied two encoders: ROM and Fat tree. The obtained results are presented using HSPICE simulator at 0.9 V power supply. The simulated data from CNTFET based converter shows significant improvements in delay and power compared with its CMOS based counterpart. The power and delay obtained from CNTFET based converter using ROM encoder are improved by 92.5% and 54% with respect to the same parameters obtained from CMOS based design while the improvements using a Fat tree encoder in CNTFET converter reaches 93% and 72% in comparison with CMOS conventional design. Manuscript profile -
Open Access Article
3 - Controller Design and Asymptotic Stability Analysis of a Buck Converter with a Cascade Control Structure Using Singular Perturbation Theory
Sajad Azarastemal Mohammad HejriThis paper presents the theoretical proof for the closed-loop asymptotic stability of a DC-DC buck converter based on singular perturbation theory. Due to the two-time scales structure of this converter with fast and slow dynamics, a cascade control structure is used to MoreThis paper presents the theoretical proof for the closed-loop asymptotic stability of a DC-DC buck converter based on singular perturbation theory. Due to the two-time scales structure of this converter with fast and slow dynamics, a cascade control structure is used to control it. This controller has two control loops: an outer loop to control the output voltage based on the proportional-integral control and an inner loop to control the inductor current based on the sliding mode control. The controllers in the loops are designed based on perturbation theory to meet the constraints of the converter and ensure the asymptotic stability of the closed-loop system over a wide range of initial conditions. For validation, the proposed control design method is simulated for a typical buck converter in the MATLAB-SIMULINK environment. The simulation results show that by properly selecting the PI controller coefficients in the outer loop, the problem requirements are met, and the asymptotic stability of the closed-loop system is guaranteed in a wide range of the converter initial conditions. Furthermore, the system robustness against load uncertainty and input disturbances as well as the voltage reference tracking are evaluated, and the proposed structure is compared with a PI-PI structure. Manuscript profile -
Open Access Article
4 - Improving On-Off Current Ratio (Ion/Ioff) in Schottky-Barrier-Type Graphene Nanoribbon FETs
Morteza GholipourSchottky-barrier-type graphene nanoribbon transistors (SB-GNRFET), despite their prominent characteristics compared to conventional transistors, have a relatively high off-current and a low Ion/Ioff ratio. In this paper, a new structure of SB-GNRFET is presented in whic MoreSchottky-barrier-type graphene nanoribbon transistors (SB-GNRFET), despite their prominent characteristics compared to conventional transistors, have a relatively high off-current and a low Ion/Ioff ratio. In this paper, a new structure of SB-GNRFET is presented in which the gate of the transistor is divided into two parts. A constant voltage is connected to the gate located on the drain side, and the gate located on the source side is the main gate of the transistor. The proposed SB-GNRFET is simulated using non-equilibrium Green functions-based numerical simulator under different geometric and physical characteristics and in biases. The simulation results show Ion/Ioff ratio improvement of up to 6.7-fold at VDS = 0.8 V. At this voltage the ratio has increased from 1.2 in the normal SB-GNRFET transistor to 8.01 in the new transistor and the off current has been reduced from 5 µA to 0.7 µA. Also at VDS = 0.6 V, as the supply voltage, the Ion/Ioff ratio increased from 3.97 to 15.8 and the off current decreased from 0.63 µA to 0.16 µA. Manuscript profile -
Open Access Article
5 - Comprehensive Optimal Management System of Distributed Resources Using Dynamic Neural Network in Modeling of Electricity Consumption Uncertainty for Grid-Connected Microgrids
Mohammad Veysi محمدرضا سلطانپور jafar Khalilpour hadi niaeiIn this paper, to enhance the optimal planning for power management of micrigrids, a strategy is proposed using power sharing through coordination between microgrids and the neighborhood system, which has no additional costs for generating units. The uncertainty values MoreIn this paper, to enhance the optimal planning for power management of micrigrids, a strategy is proposed using power sharing through coordination between microgrids and the neighborhood system, which has no additional costs for generating units. The uncertainty values of electrical consumers are modeled by dynamic neural network, considering the implementation process and high accuracy of forecasting. In another view, to supply the electrical energy of microgrid, diesel generator, renewable energies such as solar energy and wind energy and so, battery energy storage are used, in addition to the upstream grid connection. As well as, using of the reliability factors, along with a detailed assessment of current costs will improve the performance of microgrid. Hence, the loss of power supply probability (LPSP) and loss of load expectations (LOLE) are expressed as factors for assessing the accuracy of current costs. The proposed model is implemented in GAMS and MATLAB environment and the simulation results clearly demonstrate the desired performance of the proposed algorithm, and leads to gaining revenue for the under-study system. Manuscript profile -
Open Access Article
6 - H∞ Robust Stability Augmentation System Design by Genetic Optimal Coefficient for HUAV MIMO Model with Coupled Dynamics
zahra salamati zahra nejati alireza farajiNowadays, Unmanned helicopters are used widely in many applications because they have high maneuverability and can take off and landing in many areas, and its stability has special importance. Without stability augmentation system (SAS), the helicopter is not maneuverab MoreNowadays, Unmanned helicopters are used widely in many applications because they have high maneuverability and can take off and landing in many areas, and its stability has special importance. Without stability augmentation system (SAS), the helicopter is not maneuverable. Stability augmentation system or SAS design for helicopter decreases disturbances effects and improve performance. In this paper a robust SAS is designed for nonlinear dynamic model of ANCL helicopter in hover mode, this model is unstable, multivariable, under-actuated with coupling between dynamics Due to specific characteristics for liner model of the system in this paper, some filters are designed for input signals of actuators for decoupling of system dynamics in closed loop system, so these loops will become decoupled. PI controller is conventional to design of SAS in small helicopters, so PI coefficients are designed robustly for each decoupled control loop and this is designed by H_∞ Robust problem and optimized by genetic algorithm. Finally, obtained controllers are simulated for nonlinear model helicopter in hover mode that results show robustness against of nonlinear model uncertainty and disturbances. Manuscript profile -
Open Access Article
7 - New Structure of Wind-PV Farm with Improved Performance under Voltage and Frequency Fault Conditions
Mehrdad Tarafdar Hagh Farshid Najaty MazgarIn this paper a new structure for wind – PV farm is proposed. The PV arrays and DC loads are capable to connect to the proposed structure. In the proposed structure each DFIG wind turbine is connected to the AC grid through its stator windings and has a connection to a MoreIn this paper a new structure for wind – PV farm is proposed. The PV arrays and DC loads are capable to connect to the proposed structure. In the proposed structure each DFIG wind turbine is connected to the AC grid through its stator windings and has a connection to a common DC link via its rotor side converters. The proposed structure uses a high power grid side converter and an energy storage system for entire wind – PV farm. The converter power loss decrease and lifetime increase of power switches are some advantages of the proposed structure under normal operation conditions. The proposed structure with the coordinated power control of DFIG wind turbines, the ESS and PV arrays improves the low voltage ride-through capability under-voltage fault conditions and enhances the frequency response of the wind farm under frequency faults. The proposed structure is simulated in MATLAB/ Simulink software and the results are presented. Furthermore, an experimental setup is provided to test the operation of the proposed structure. Manuscript profile -
Open Access Article
8 - Energy Efficiency in Secrecy Multi-Antenna Two-Way Relay Networks
F. B. soroush akhlaghipaper investigates the energy-efficiency in secrecy two-way relay networks. It is assumed that in the presence of several multi-antenna amplify-and-forward relays and a single eavesdropper, two single-antenna users exchange their confidential messages during two hops. I Morepaper investigates the energy-efficiency in secrecy two-way relay networks. It is assumed that in the presence of several multi-antenna amplify-and-forward relays and a single eavesdropper, two single-antenna users exchange their confidential messages during two hops. In the first hop, both users send their messages to the relay nodes and during the second hop, the relays send the received signal to the users by using the beamforming matrix, to minimize the received information by the eavesdropper .In this way, using two beamforming strategies, named as Null-Space Beamforming (NSBF) and Information Leakage Alignment Beamforming (ILABF), the secrecy energy efficiency that is the ratio of total secrecy sum-rate to the total power consumption of the network is calculated. It is shown that the aforementioned problem is non-convex so it will be converted to the convex form, using the Semi-Definite Relaxation (SDR). This problem has not closed-form and is solved using the interior point method.In numerical results, it is observed that by using the information leakage alignment beamforming (ILABF) method, energy efficiency is allocated more value than the null-space beamforming (NSBF) approach that was used in previous studies. Manuscript profile