Sharif Digital Repository

Frequency scarcity has emerged the necessity of opportunistic utilization of frequency bands, which can be realized through a cognitive radio system. During an agile communication between unlicensed users, a cognitive radio system must avoid collision with licensed users. Hence it should continuously observe the band of interest and report the presence of licensed user signals. This task is fulfilled by a vital part of a cognitive radio system, called the spectrum sensing core. Recently several techniques have been proposed for the spectrum sensing in literature. Some of them like matched filtering, cyclostationarity based detection are based on primary user signal features. However energy... 

The application of deep learning algorithms in the processing of telecommunication signals is increasing. One of the issues in this area is the automatic recognition of radio signal modulation. Recognizing the type of signal modulation as the first stage of baseband signal processing on the receiver side is a key issue in military and civilian applications. The problem with classical algorithms for solving this problem is their strong dependence on channel characteristics and factors resulting from the transmitter and receiver being non-ideal. However, modern algorithms based on deep neural networks have been able to make the model somewhat resistant to these factors. However, the detection... 

Today, the “wireless” is used almost synonymously with radio-frequency (RF) technologies as a result of the wide-scale deployment and utilization of wireless RF devices and systems. The RF band ranges from 300 kHz to 300 GHz and its use is regulated by regional and international agencies. With the ever-growing popularity of data-heavy wireless communications, wireless products and services, the demand for RF spectrum is outstripping supply, which causes the spectrum congestion. Therefore, the time has come to seriously consider other viable options for wireless communication using the upper parts of the electromagnetic spectrum. In this way, the optical band which includes infrared, visible,... 

In response to the threat of terrorism, people are checked at security checkpoints. Like airports, places of pilgrimage have become increasingly important. Millimeter wave imaging systems are one type of system used; these systems have the ability to detect hidden items. Based on this technology, cylindrical and Cartesian body scanning devices have been commercialized. In cylindrical imaging, all aspects of the body are examined, and the output of this type of imaging is a sequence of images showing different views of a person. These body scanners use object detection neural networks to speed up the process of examining people. Also, in order to protect the privacy of individuals, their... 

Nowadays millimeter wave imaging technology has found various applications in industry, medical and security systems. From one side the capability of penetration of this frequency spectrum into non-metal objects, and being harmless to humankind on the other side, has made this spectrum an appropriate alternative instead of dangerous spectrums such as X-ray. Recently, development of millimeter wave electronic circuits and antenna arrays has made the optimal design and implementation of millimeter wave imaging systems feasible. Among actions which have been taken in industry, medical and security systems until now, we can refer to efforts for detection of defects in production line,... 

Blend of Polycarbonate/ poly(butylene terephthalate) is among the most famous blends of polycarbonate/polyester with vast engineering applications and unique properties. Miscibility and compatibilization of this blend are important as they directly influence the general properties.Transesterification which occurs in the melt state, is a series of cutting and rejoining of dissimilar polymer chains. The reaction ruins the order of pure chains and forms block copolymers of different natures. Further progress in transesterification lead into a completely random copolymer of initial chains. Time, temperature and addition of catalyst can effectively influence transesterification.In this study,... 

It is well known that arrays of antennas make it possible to steer the radiation pattern without steering a physical structure. For the past few decades this has been considered for many civil and military communication systems. Recently, ultra-short pulses are considered for high resolution radars and ultra-wideband communication systems. Systems with short pulses and large antenna arrays may benefit from high resolution in both temporal and spatial domains. But the implementation of the ultra-wideband feeding circuits for such antenna arrays is a hard job even with state of the art electronics. Optical technology has been applied, successfully, to a number of radio applications such as... 

This research examines the importance and implementation of incident management and problem management processes in the field of software development systems. In the fast-paced and dynamic world of software development, incidents and problems can arise that disrupt system performance and impact customer satisfaction. Incident management provides a structured approach to quickly identify, prioritize, and resolve unexpected events, while problem management focuses on identifying root causes and preventing the recurrence of incidents. By addressing the key stages of these processes and their benefits, the research emphasizes the importance of proactive incident resolution, software quality...