نشریه صنایع الکترونیک
سال نهم شماره 4 (پیاپی 36، زمستان 1397)

In this paper, the two novel reconfigurable polarized microstrip antennas with capability of switch between linear and circular polarization are presented. The main idea in this work is using some narrow graphene strips, as variable surface impedance, in the middle and the edges of a traditional square patch. The graphene strips are activated and deactivated by applying the two different DC voltages. Based on surface conductivity of graphene, the surface impedance of these strips are calculated in both of active and deactivate modes. The simulated results show that the polarization of the proposed antennas can be changed in two or three different cases in the frequency of X band. As a main advantage of the proposed antennas, the change of graphene bias voltage has no destructive effect on radiation patterns and antenna input impedance. In addition, the DC bias voltage of the graphene surfaces in active mode are not high.

In this paper we propose a new resource allocation framework for unmanned aerial vehicle (UAV)-based cooperative networks. In the considered network, three node exist: one transmitter and two receivers. In addition, we assume that a UAV is used in the network as a decode-and-forward (DF) relay. For the channel model, we only consider the path-loss. We assume that the information transmission is performed only when a line-of-sight (LoS) connection could be established between communicating parties. The UAV moves from the transmitter towards the receivers. UAV receives the information from the transmitter, and when it approaches to the receivers, it simultaneously transmits information intended for both the receivers using non-orthogonal multiple access (NOMA) technique. The resulting optimization problem is non-convex and hard to solve. To tackle the problem, we adopt the successive convex approximation (SCA) technique where the original problem is approximated by a convex problem which could be solved easily using existing optimization tools like CVX. Finally, the proposed framework is evaluated using simulation for different network parameters. Simulation results confirm the efficiency of the proposed scheme.

In this article, an optical switch has been proposed and simulated by designing and embedding a parity-time (PT) symmetric coupler inside one of the arms of a multi-mode interference (MMI) based Mach-Zehnder. The whole structure consists of two MMI couplers at the beginning and end of the structure so that they are connected to each other through two passive waveguides, also a PT-symmetric coupler embedded in one of the arms. All elements in the proposed switch are linear and based on PT-symmetric coupler status; optical switch operates in two passive (without gain/loss) and active (with gain/loss) states. The suggested switch finds the extinction ratio and for active and passive states, respectively. Furthermore, regarding the simulation results, the insertion losses are given rise to low values for different gates. In this article, an optical switch has been proposed and simulated by designing and embedding a parity-time (PT) symmetric coupler inside one of the arms of a multi-mode interference (MMI) based Mach-Zehnder. The whole structure consists of two MMI couplers at the beginning and end of the structure so that they are connected to each other through two passive waveguides, also a PT-symmetric coupler embedded in one of the arms. All elements in the proposed switch are linear and based on PT-symmetric coupler status; optical switch operates in two passive (without gain/loss) and active (with gain/loss) states. The suggested switch finds the extinction ratio and for active and passive states, respectively. Furthermore,

Wireless sensor networks have attracted a great deal of attention as one of the key enabling technologies for 5G cellular networks. One of the main challenges ahead of such networks is limitation of energy resources which directly affects their lifespan. In this paper, an adaptive coding technique for wireless sensor networks is presented. On the contrary to the previous studies which have considered block fading channels, where a constant fading factor is assumed during the transmission of a block of data, we track slow time variations that channel experiences during the transmission of a block of data. We design an adaptive coding technique for this case. The proposed algorithm is based on iterative decoding and aims to achieve an error probability lower than the permissible threshold while minimizing the energy consumption. Our simulation results, employing Hamming codes, demonstrate that the proposed adaptive coding scheme, decreases the power consumption and consequently increases the network lifespan.

Massive MIMO system is one of the advanced and attractive technologies for fifth generation of wireless networks. In such systems, base stations employ a very large number of antennas (Hundreds or even thousands of antennas). As a result, in these systems, capacity, spectral efficiency and energy efficiency increases in comparison with conventional MIMO systems. In the channel estimation, interference, which is produced by reuse of the same pilot sequences by different users of neighboring cells, is the most important factor in the performance limits. This phenomenon is referred to as pilot contamination. In this paper, pilot contamination is described and then the research works presented by the researchers on this topic has summarized. We categorize the different proposed mitigation techniques for pilot contamination using the following taxonomy: protocol-based methods, precoding methods, AOA-based methods, blind methods and smart pilot assignment methods. Finally, we propose a method based on smart pilot allocation, to reduce pilot contamination. Simulation results show that both uplink rate of user’s increases based on the proposed method and the accuracy of channel estimation improved greatly than exciting methods. Then we propose a method based on pilot precoding and protocol based allocation to reducing pilot contamination effects. In addition, we study a range of challenges and future research topics.

One of the fundamental limitations in terahertz and optical imaging, is the spatial resolution limited to half of the wavelength which is caused by the wave nature of light, and is known as the Rayleigh diffraction limit. Such resolution is insufficient for the study of many objects and phenomena including biological cells, mobile carriers in semiconductor nano-devices, as well as heat transfer and electromagnetic interference phenomena in nano-electronic circuits. In recent decades, some efforts have been made to introduce and develop techniques to overcome this limitation, including methods based on using near-field and detecting evanescent waves. In most of the proposed methods, a near-field probe is used to concentrate the field near the sample, and to couple the near-field (evanescent field) into radiation or propagating wave. In this paper, with an emphasis on the fundamental aspects of the near-field technique, we review, investigate, and work on a harmonized set of basic definitions associated with near-field imaging. The diffraction limit and its theoretical origin, the applications of near-field imaging, possibility to achieve sub-wavelength resolution in accordance with Heisenberg uncertainty principle have been explored. Finally, by describing the design process of three near-field imaging probes, their capabilities are investigated.

In the field of digital electronics, it is very important to achieve faster and less power consuming circuits. Hence, improvements in the implementation of computational circuits, such as multipliers which are widely used in microprocessors, signal processing, and many cryptographic algorithms, are considered. In addition, the compressors are the most important operation unit in the multipliers. Amongst different compressors, compressor (4;2) is one of the most popular methods to implement of multipliers. Moreover, the implementation of this compressor depends primarily on XOR gates, and an appropriate XOR design is effectively improving the performance of compressor (4;2) and it can improve the overall performance of the multiplier system. In this paper, the design of compressor (4;2) is based on the proposed XOR gate with carbon nanotube transistors, which has been simulated in 32 nm CNTFET Stanford technology. Simulation results , shows that the proposed design, while reducing the circuit area, improve delay by 4.31% , power consumption by 45.99% and power delay product by 47.72%, in comparison with the best compressors.

The security of the mobile devices has become a major issue since hackers target them through malwares in order to harm the systems or gather sensitive information and get access to the systems remotely. Recently, new ways have been introduced to confront malwares and other viruses. Two main techniques for recognizing malwares are dynamic analysis and static analysis. This paper proposes a new method using the static analysis to help improve the accuracy of the malwares in detecting threats faster and with lower processing time. For this purpose, our suggested method has utilized the android application’s main components to recognize the malwares using the machine learning algorithms. Furthermore, our method has used the feature selection algorithms to reduce the processing overload and to enhance the speed and accuracy. Our method have used the following components as the classification features in our suggested algorithms: API calls, Intents, network address and IPs, services and provider, activities and permissions. In addition to these individual features, our method has also employed complex features to improve malware recognition. We have used 123,446 software and 5,561 malwares to evaluate the accuracy and the precision of the suggested method, demonstrating to be 99.4 percent.