مجله علوم و فناوری های پدافند نوین
سال سوم شماره 4 (پیاپی 10، زمستان 1391)

Nowadays, most optical communication systems use semiconductor lasers as optical sources, but in FSO systems, due to high transmission channel loss, optimum usage of this kind of laser is essential. Increase of bit error rate is not only due to transmission channel losses, but, in some cases it could be due to instability of laser power or drifting of laser characteristics due to aging. Driving semiconductor lasers, monitoring and controlling power and temperature are important aspects of FSO systems. In this paper, a system able to stabilize output light power intensity of semiconductor laser (0.1 percent maximum error) for variable environmental temperature (0 to 50 ̊C) is designed and built.

Considering the rapid advances in high quality mobile devices, knowledge transfer over mobile network has become a growing field of research. The major problem in knowledge transfer system in mobile environment is to deliver the needed knowledge to the user for decision making in the right time and right context. The problem of knowledge transfer in the "right time" has been studied previously, but less attention has been paid to the problem of knowledge transfer considering the "right context". In this paper, the problem of knowledge transfer in the mobile environment, according to the context information is discussed. An architecture is proposed for knowledge management system in a mobile network based on GPS to predict the road traffic congestion and to guide derivers. The anticipation of traffic condition helps traffic managers to avoid the negative consequences of high traffic hours.

One of the most important issues in passive defence is the design of bullet penetration resistant structures and panels. Two-component ceramic-composite armors are widely used in the bulletproof panels. In the recent decades, optimum design of thickness and material of ceramic and composite has been seriously considered by ballistic experts. Florence analytical model provides a good prediction of ballistic limit velocity of ceramic-composite armors. In this paper, based on the Florence and Bendor model, an effective methodology for optimum design of two-component ceramic-composite armors is presented, by a genetic algorithm solving technique. The design goal is achieving a minimum areal density for a given ballistic limit velocity of armor. The criterion is having the highest level of protection. In this method, material and thickness of ceramic and composite layers are considered as the design parameters. Using the results of the optimal solution, armors are designed to be resistant against two types of bullets with 7.62 and 12.7 mm caliber for different distances from target to firing place.

Today, physical expansion and high density of great cities, due to narrow access roads, large distance from medical care centers and location at areas with high seismic risk, will lead to a perilous and unpredictable situation in case of the air raids Occurrence of air raids to these cities, along with lack of attention to principles of passive defence will destroy the functionality of street networks and cause large amount of casualties and financial damages. Zone 6 of Tehran, with 220,000 population and 20 km2 area, is one of the main municipal zones of Tehran. In this paper, vulnerability degree of street networks in zone 6 against the air raids is calculated through overlaying maps and data in combination with IHWP method and GIS. The results shown that moving on from north to south of the zone, the vulnerability increases. Likewise, highways and streets with substantial width and low building and population density hold little values of vulnerability.

In recent years, different networks for information transmission have been emerged. Multimedia information like video take much storage volume. This high storage volume needs high bandwidth, high electrical and computational power to process and transmission of data, which is not possible in many networks. For example, wireless multimedia sensor networks that have constraints in their resources like memory, bandwidth and energy consumption can be mentioned. In this paper, a system for environment monitoring consisting of a transmitter network, a receiver network and a base station with a transcoder has been introduced. In the proposed method, compression has been achieved using transcoding. This method has resulted in increasing of compression along with keeping the video quality and reduction of calculation complexity in coder and decoder. The simulation results of this method have been compared to classic video compression methods and the superiority of the proposed method has been presented.

Taking measures to reduce vulnerabilities of industrial and living centers and sustaining their activities in crisis times is essential. In this line, buried and underground structures are among the most important elements required for preserving vital manufacturing centers in times of crisis. In order to build such space, it is essential to examine the industry to be relocated before embarking on any action as a result of the costs and difficulty associated with implementation works. That is, product type, manufacturing process, the kind of required equipment and machineries as well as specialists should be analyzed in the first place. Then, by selecting the right key points of manufacturing process, those parts that are of significant importance and cannot be outsourced are moved into the structure. In this study, once major criteria for constructing the buried structure are identified, they are examined and monitored using analytical hierarchical process (AHP). Then, as a case study, unmanned aerial vehicle industry is studied to achieve a set of principles and criteria for designing industrial production line within the context of a buried secure space. Through analyzing the overall production process, key part of the industry is identified so that it could be transferred into the buried space.

This article proposes a method to classify digital modulation type from ASK, PSK and FSK groups, without prior information of received signal. This method has two steps and is called "clustering method". In the first step, the modulation group, and in the second step, modulation order is determined. Using clustering method, the least pre-processing, the most effective separation characteristics and appropriate classifiers was applied to each group and genetic algorithm has been used to improve system performance. The advantages of this method are high accuracy of identification, simplicity, blind identification and more modulation candidates compared to other similar methods.

While many research papers exists about radar signal estimation using ELINT gathered data, no deep research exists about radar performance evaluation, using collected data. This important topic is regarded in this paper using some physical basic laws of radar and signal processing as well as some logical interpretations. Estimated parameters include antenna beamwidth, gain and physical dimension, range and angle resolution, clutter attenuation level, minimum detectable RCS, maximum detection range, transmitted and consumed power. Some estimation about radar performance parameters, real data about some well-known radar systems are presented and it is shown that, the proposed algorithms prepare almost accurate estimation of radar parameters.