فهرست مطالب

Majlesi Journal of Electrical Engineering - Volume:2 Issue: 2, 2008
  • Volume:2 Issue: 2, 2008
  • 80 صفحه،
  • تاریخ انتشار: 1387/09/20
  • تعداد عناوین: 9
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  • Hosein Khaleghi-Bizaki, Mohammad Jabbariani, Nader Ghadimi Page 1
    Match filter is one of the important parts of radar receiver. By using of Match Filter, the signal to noise ratio can be maximized so that the probability of detection is increased. Match Filter can be used as a pulse compression filter in radar receiver. Binary phase code is one of the pulse compression methods that, the compression can be down with a Match Filter in the receiver. Doppler effect is one of the problems that degrade the performance of Match Filter. In this paper, two methods “Mixer Array” and “Segmented Match Filter” are proposed for Doppler compensation. The operation of these two methods as Doppler compensation techniques are considered theoretically. The simulation is used to demonstrate the Doppler compensation performance of new techniques compared to conventional methods.
  • Marzieh Varposhti, Naser-Movahhedinia Movahhedinia Page 7
    Transferring real-time traffic such as voice and video over wireless LAN network (WLAN) requires stringent delay and jitter requirements. One of the methods to provide QoS in this standard is Enhanced Distributed Channel Access (EDCA) which benefits form the concept of traffic categories. However, EDCA is a contention based method; therefore it can not guarantee strict QoS required by real-time services without proper network control mechanisms. One of the challenging problems in wireless networks is the failure of transmitting media due to fading. Normally the node does not differentiate between the media access collision and the channel failure.The performance of this method in case of fading channel has not yet been evaluated. In this paper, we analyze the effect of loss and delay caused by fading channel on EDCA performance. Then, we propose a modification to the media access scheme to elevate the performance against channel failures. Moreover an adjustment for the maximum number of retransmissions is proposed to maintain the delay and jitter requirements of the real-time traffic. The performances of the proposed methods are evaluated by simulations.
  • Ali Pour Yazdanpanah, Karim Faez Page 15
    Analysis of person’s behavioral and psychological features like Gait or the manner of walking, allows human identification process to be able to extract the gait information from a video sequence of different persons at a distance and recognize the specific person. This paper proposes a fast gait recognition algorithm based on the averaged silhouette of person. Three important novelties in our proposed algorithm cause that it gives a better performance than previous methods in both recognition rate and computational speed.1- frame sampling method, which causes the algorithm computational time, without any change in recognition rate, decrease to about half. 2- New method for background estimation, which gives an acceptable estimate of the background. 3- Local thresholding method, which gives more complete and more accurate binary silhouette pictures. Experimental results demonstrate that our proposed algorithm accuracy is superior to other previous methods in the gait recognition application.
  • Sayedmohamad Madani, Emadedin Saremian, Kamran Shafafi Page 25
    grid connected wind turbine is daily increasing. a problem in power grid is grid faults.most problem is system stability after faults, also a probable problem of new energy sources in connection with grid is Islanding due to faults.in this condition loading mismatch between generation and load ‏consumption in isolated part of system can cause voltage and frequency cross it’s allowable limit.too in the case of over generation rotor will accelerate.so these lead to turbine interruption.in this paper wind turbine equipped with doubly fed induction generator is controlled for uninterrupted operation during fault to achieve more stability and rapid voltage recovery. Authority of DFIG grid side converter and Dstatcom effect after three phase short circuit fault are compared. results shows that with combination Dstatcom with grid side converter, voltage regulation in normal operation is beter.also after a fault more voltage stability and rather voltage recovery is achieved.too a suitable control will be presented for sake that wind turbine be able under Islanding operation to feeding local load at rated voltage and rated frequency.ability of control strategy in Islanding operation is investigated and simulation results Illustrate control strategy ability.
  • Hamidreza Fardad, Behrouz Shahgholighahfarokhi, Hadi Khosravi Page 35
    Resilient Packet Ring (RPR) is a new kind of metropolitan area network which technically provides complete flexibility in defining service classes that can be sold to the end user. On the other side, the IETF Diffserv group has created specific definitions for class based services over IP networks. Hereby, we are going to propose a more effective queuing for RPR which considers the mapping between DiffServ and RPR QOS provisioning mechanisms. This novel method is used to support the requested quality for IP over RPR delivery. Only the standard PHBs have been considered for such a mapping consisting EF (expedited forwarding), AF (assured forwarding), and default PHB. The EF class is preferred to be transmitted via class A, while AF class is more distinctive. AF includes four different flows each including up to three drop precedence. To improve the quality for AF flows, we have proposed a multi-level queuing method considering different levels of drop precedence. The default PHB is also preferred to be mapped as class C traffic. Our proposed method has been investigated using some simulations over NS2. The simulation results have shown superior performance in terms of loss and delay parameters.
  • Mohammad Sheikhzefreh, Pejman Khadivi Page 45
    Oceanographic data collection, pollution monitoring, offshore exploration, disaster prevention, assisted navigation and tactical surveillance are some of the applications of underwater networks. Underwater networks should send the gathered information to other users or an offshore station via a base station in the sea. Since the available bandwidth in underwater is severely limited, frequency reuse and cellular networks concepts are very important. In this paper, after driving the ratio of signal to interference for underwater acoustic channels, the constraints for the cell radius are determined. One of the important results of this work is that, for special parameters like bandwidth, it may be impossible to provide the required signal to interference ratio and bandwidth for the network users. Furthermore, in this paper, number of supportable users, per-user bandwidth, and the user capacity for a cellular underwater network are determined.
  • Majid Delshad Page 51
    In this paper a new zero voltage switching current fed half bridge converter with an auxiliary circuit is proposed. The auxiliary circuit not only absorbs the voltage surge across switches at turn off instance, but also provides zero voltage switching condition for all converter switches. Therefore in this converter the efficiency is higher than hard switching counterpart and also main switches voltage stresses decrease. Since the switches in auxiliary circuit operate under soft switching conditions, these switches don’t apply additional losses to proposed converter. Implementation of control circuit is very simple since the converter is PWM controlled and the auxiliary switches turn on are complementary with respect to main switches. In this paper the proposed converter operating modes are analyzed and simulation results are presented. To verify the converter operation a 100W laboratory prototype operating at 100kHz is implemented and the experimental results are presented.
  • Jvad Ebrahimnejad, Rasoul Amirfattahi, Farzaneh Shayegh Page 59
    In this paper we describe the lung nodule detection through image processing methods. Therefore, in the preprocessing stage, we use a medical-like method to omit all objects that surely they are not nodule. In this way nodule candidates are obtained. Therefore, false positives decay, while rate of main process does not increase. Finally, nodule candidates are selected through these suspicious regions. In the first step, we extracted candidate areas of the lung using synchronous thresholding in consecutive slices, medical decision implementation and also morphology methods. We divided the preprocessing stage into two phases for detecting all of lung nodules more accurately, depend on the nodule is connected to lung wall or vessel or it is an alone nodule. Here, template matching and maximum similarity method have used for nodule detection. The used database comes from LIDC database images that consist of 7 patient's CT scans. All of nodules are completely detected and there are 3 FP/slice. Value of similarity has been computed for all of points (pixels) that determined in preprocessing stage. Indeed, the limited search area makes the optimum (i.e. direct search) algorithm as fast as other sub-optimal search methods. Indeed, this method is faster than other methods that don’t have enough attention to information of CT scan slices.