JOURNAL OF IRANIAN ASSOCIATION OF ELECTRICAL AND ELECTRONICS ENGINEERS
Year:2021 | Volume:18 | Issue:3|Papers Count:18

Radio Telecommunication between satellites and ground stations is considered as one of the key parts of space missions. Since controlling a satellite is carried out using Telemetry-Telecommand (TT&C) and positioning links, these two satellite links are crucial. Unlike ground antennas, there are many requirements in designing space antennas depending on the type of communication. Due to the rotation of the satellite around the Earth and the need to maintain the communication with the satellite, one of the most important requirements in designing TT&C and positioning links antennas is to create a relatively omnidirectional radiation pattern with circular polarization to cover at least 300 degrees of space. On the other hand, the location of antennas on the satellite, type of satellite structure and dimension considering mass budget constraints are other important challenges which determine the antenna layout and location, as well as the antenna type. In this paper, the challenges in designing the TT&C and positioning links antennas for a remote sensing satellite in VHF and UHF frequency bands are investigated, then the designed antennas are fabricated. Finally, the simulation and test results are compared.

In this paper, a new wideband horn antenna based on the substrate integrated waveguide (SIW) technology fed by GCPW structure with compact size(3. 38λ 0*2. 65λ 0*0. 14λ 0) is designed. The proposed antenna is fabricated by using two Rogers RT 6002 with the same height of 1. 524mm (total thickness of 0. 14λ 0 at the center frequency) and ε r=2. 94. The proposed antenna utilizes a suitable wideband transition in the feed section and an arc-shaped metal taper printed on the extended dielectric slab with two metal posts in the horn section. By using the proposed antenna, a wide impedance bandwidth without using ridged structures is obtained. The designed antenna has a VSWR less than 2. 5 across a broad frequency range 8-19. 5 GHz and show acceptable and stable radiation patterns in the same frequency range.

In this paper, the minimax optimization method has been proposed to design the shaped dual reflector antenna for being used in the geostationary satellite (GEO). For this purpose, the distortion on the reflector surface is considered with an expansion of B-spline functions and the coefficients of expansion are obtained using the minimax optimization method. In comparison with other optimization methods, which are based on evolutionary algorithms that prolong the antenna design, this is a gradient-based method and significantly accelerates the antenna design. In the minimax optimization method, there is a need for calculating the derivatives of the optimization fitness function compared to the problem variables. Thus, in this paper, the derivative of the fields calculated by physical optic have been analytically calculated compared to the reflector surface variables. A comparison of the simulation results and implementation time of two minimax methods with the genetic algorithm indicates the high efficiency and rate of minimax method.

Pyramidal absorbers that are put on the floor of a semi-anechoic chamber are exposed to abrasion due to their frequent move. In this paper, we propose a base inside which an absorber is placed. The proposed base is made of MDF and does not degrade the performance of the absorber. In addition, this base prevents direct hand contact to the absorbers when carrying them and hence increases the absorberschr('39') lifetime. Simulation results show that the proposed structure provides acceptable performance. As well, measurements in a semi-anechoic chamber prove that the absorbers placed inside the base still satisfy well the requirements for standard electromagnetic compatibility susceptibility tests.

A novel higher order mode excitation method for a 8×8 cavity-backed slot array antenna in Ku-Band is introduced in this letter. The antenna is formed by three main layers, consisting power divider, slotted cavities, and dipoles. All the 64 elements of the array is simply excited by a coaxial probe located at the center of the ground plane. The power divider distributes the electromagnetic waves into the upper four cavities, which leads to the excitation of TE440 mode in each cavity. The fabricated antenna exhibits a maximum gain of 19. 6dBi and radiation efficiency of 80%. The measured S11<-10 dB is in the range of 14. 1-14. 3 GH. Moreover, the aperture efficiency of this antenna reached a peak of 72%.

In this paper, a method is presented to design the Cassegrain antenna dimensions and feed antenna in order to optimize antenna blockage efficiency. The special case in which the feed antenna is placed behind the main reflector is investigated and conical corrugated horn antenna is used as the feed antenna. A mathematical equation is extracted to obtain optimum value of the angle of incident waves from the feed antenna to subreflector edge. This equation is then rewritten as an error function and optimization Toolbox of MATLAB software is used to minimize this error function. After solving this equation, by using the governing relations, the other physical parameters of the antenna can be extracted and a design example is presented to further illustration of the problem in 20 GHz at K-band. In this example, slant factor of the horn is assumed arbitrarily equal to 0. 32 and optimum dimensions of antenna are calculated. In continue, this design example is solved for different slant factor values and the effects on various parameters of antenna such as subreflector diameter, antenna magnification factor and horn slant radious are investigated.

In the fiber amplifiers, the initial values of pump and signal powers are specified. so; Solving rate equation in the fiber amplifiers includes initial value problems. In the fiber lasers, the initial value of the pump is known but signal (laser) power must be determined. Hence; solving the rate equation in the fiber lasers is the part of the boundary problems. Different methods are presented for solving boundary value problems. In this paper, using the shooting method, a proper region introduced as answer range and solutions for rate equations of fiber laser and amplifier have been found. The advantage of this method is that to start calculation, we do not need the accurate initial guesses. With the proposed method, different forward, backward and bidirectional pump schema in Ytterbium doped fiber laser is verified. The parametric optimum length is introduced in high pump power with simplification in rate equations. In this paper we introduced a new definition of optimum length in conventional pump power fiber lasers and effects of background loss verified in the optimum length.

The design and simulation of optical switches is of great importance due to the optimal use of the bandwidth and bandwidth available in telecommunication networks. The subject of this article includes the design and simulation of microprocessor resonators and all-light switches with graphene adjustment. In fact, this paper evaluates the optical switches based on the microstructure of the resonator and their electro-optical adjustment by applying voltage to the applied graphene layer. The designed switch has a high scale due to its micrometer size. In fact, in this article, by designing different micro-circuit structures of resonators, optical switch with decreasing coefficient and wide bandwidth has been designed.

The spectral sensor provides one of the components of opportunistic access to frequency resources. These sensors must measure the ambient spectrum with high accuracy in a short time. It is important to use methods and algorithms that can be implemented in practice; therefore, the complexity of the calculations should be reduced as much as possible. Detection performance is hampered by issues such as shadow effects, blurring, and multi-directionally; therefore, to overcome these problems and the unavailability of information about the signals received by the primary users and the power level and noise of the received signals, methods such as using several antennas in the spectral sensor, resisting spectroscopic methods against indeterminate noise, are used. In this paper, different criteria for decision making and determining the appropriate threshold by extracting special values of the covariance matrix are investigated. Also, by calculating a few moments from the detector to the maximum to minimum values of the MME covariance matrix by the proposed standard GEV distribution, simulations are performed and the results are compared with the Tracy-Widom distribution. The results of the simulations with a limited number of 4 antennas indicate the probability of signal detection in SNR with-30dB, which has increased the accuracy by 3dB compared to the Tracy-Widom distribution. To evaluate the efficiency of this method for hardware execution, the results of the proposed algorithm have been reviewed and implemented by an FPGA array processor along with a processor with XILINX ARM architecture, which is called the systems embedded in the SOC chip.

This paper investigates the problem of image steganography. The existing algorithms provide low performance due to disregarding the structure and properties of images. Furthermore, most of these schemes are lossy. Considering the shortcomings of the previous algorithms, we propose an effective algorithm, namely Lossless and High Capacity Image Steganography (LHCIS), which embeds the secret image into the cover image losslessly. The proposed scheme comprises secret image compression and embedding the compressed image into the cover image using the LSB algorithm. The compression procedure includes two phases. The first phase constructs the corresponding difference image to the given secret image. The mentioned image represents the variations of the adjacent pixels of the secret one. Each pixel of this image is derived by subtracting its corresponding pixel in the secret image from the adjacent one. The difference image is encoded to reduce its storage space in the second phase. The compression ratio is high due to the small values of the pixels of the difference image. According to the performed simulations, LHCIS increases the embedding capacity by 40%. Furthermore, it improves the PSNR of the stego image by 2. 16 in comparison to the previous algorithms.

Today, video conferencing is one of the most sought after features of the Internet. The purpose of routing algorithms in online video conferencing is to increase the number of requests accepted according to Quality of Service (QoS) satisfaction. Most research in this field focuses solely on bandwidth, and relatively few studies consider both bandwidth and delay constraints. In this paper, we propose a new routing algorithm in the context of MPLS networks with fuzzy rules approach that considers both bandwidth limitation and end-to-end delay (bandwidth-delay) for path searches. The fuzzy system is a fuzzy weighted prediction model for filtering high resource requests. A combination of traditional routing and MPLS improves the mobility mechanism, scalability and overall network performance. We name the proposed algorithm as Fuzzy Bandwidth and Delay Routing Algorithm (FBDRA). The FBDRA is attempting to delay requests with high bandwidth and maximum end-to-end delay. We will use Matlab R2017a to simulate many different scenarios and measure criteria such as the number of requests received, average route length, and load balancing. In addition, we compare the performance of FBDRA compared to some of the previous related work such as MHA, WSP, MIRA, BCRA, MIRAD, BGDG, BGLC, SAMCRA and MDMF. The simulation results show that the FBDRA provides the best performance for video conferencing.

Haplotype estimates based on DNA information are used to detect human genetic diseases. This problem can be modeled in the genomic processing of signals as a low-rank matrix in which only a few elements are observed. As a result, an effective way to estimate the haplotype from incomplete observations is to use matrix completion methods. In this paper, using matrix completion methods, an attempt has been made to estimate the haplotype through matrix factorization. In references, the reduction gradient method has been used to solve the problem. However, in the previous methods, outliers were also included in the calculations, which caused an error in the haplotype estimation. In other words, these methods do not pay attention to the existing conditions for haplotype matrices, and this has led to outdated estimates for haplotypes. In this paper, with the matrix completion method and considering these conditions in the haplotype matrix, we introduce a new cost function as a penalty expression for haplotype estimation. The new expression added to the cost function reduces the effect of skewed data and thus increases the accuracy of haplotype estimates. The simulation results confirm the need to reduce the haplotype retrieval error

In this paper, we propose a feedback-based differential signaling scheme (DSSFB) for the 2x2-free-space optical (FSO) system that is exposed to an atmospheric turbulence channel with pointing errors. We obtain closed-form expressions for the average bit error rate (BER) performance of DSSFB scheme using power series form of probability density function of channel, and then we compare it to differential signaling scheme (DSS), single-input dual-output system, and repetition coding (RC) scheme. Moreover, we obtain an approximation for the BER of the proposed scheme. Numerical results, show that the proposed scheme, in contrast to the differential signaling scheme, can achieve full diversity gain, whereas in terms of coding gain it is even better than the repetition coding scheme. Finally, we investigate the effect of imperfect feedback on the performance, and we show that even with an erroneous feedback link, the DSSFB scheme outperforms the DSS scheme in terms of coding gain.

Acoustic feedback is often formed when the signal source is placed in front of the speaker. This creates an acoustic loop. Acoustic feedback reduces sound quality and produces artificial sounds. Acoustic feedback elimination methods can be used to improve Maximum Stable Gain (MSG) and sound quality. One of the approaches to deal with acoustic feedback is to use the error prediction method based on the Kalman frequency domain filter using feedback partition block. Simultaneous use of the Kalman filter in the frequency domain and the segmentation of the feedback path has improved the criterion of maximum stability compared to methods such as time domain adaptive filters or without partition block of the feedback path. But this approach does not work well in the face of noisy input. In acoustic environments, the presence of ambient noise prevents the signal from being received without noise. In this study, after preprocessing (noisy signal with Gaussian noise with standard deviation of 0. 0 to 0. 5 dB), two steps: 1. Using Kalman filter of time domain and 2. Using frequency domain Kalman filter method using partition block of the feedback path is provided to improve the MSG criterion of about 3 to 4 dB.

In this paper, an unmanned aerial vehicles (UAV)s is used to improve the physical layer security of a cooperative communication network. More specifically, in the proposed surveillance system a UAV acts as a legitimate monitor to eavesdrop on a dubious decode-and-forward relaying communication. To maximize the effective eavesdropping rate, two adaptive scenarios are suggested for the legitimate monitor: scenario I) jammer-eavesdropper, and scenario II) eavesdropper-helper/eavesdropper-eavesdropper/ eavesdropper-jammer. For each strategy, the received signal-to-interference-plus-noise ratios SINRs are derived. Numerical results reveal that the proposed strategies achieve better performance than intuitive benchmark schemes. Moreover, as a simple criterion, UAV should employ scenario II when it is close to source, and employ scenario I when it is close to relay.

Risk Assessment and Management have always been considered as one of the most challenging issues of each organization. Risk assessment would not be possible but by risk analysis of the existing vulnerabilities. Vulnerability prioritization makes it possible for security administrators to have better understanding of the infrastructure. So they would be able to find the most perilous vulnerabilities to bring cost benefit trade off into practice. Nowadays most of the attacks are the multi-step ones, in which, attacker exploits more than one vulnerability in a specified manner. So, it would be inevitable to consider the interaction of vulnerabilities for risk assessment. In this relation, the most sophisticated difficulty would be lack of standards for finding the interrelationship between vast amount of vulnerabilities and risk analysis is being done only for one step attacks. So, in this paper, a method have been introduced for risk assessment of Multi-step attacks which improves the accuracy of the existing vulnerability scoring systems.

Recently, Machine Type Communication (MTC) devices have been an attractive area of research. MTC has grown in all fields, in various technologies. In this type of communication, some of the requests are delay-sensitive and must receive to their processing in real time. Furthermore, given the high volume of information generated by the device are problems that cloud computing is used for the processing, analyzing, and storage of data from the client devices. Cloud computing services are having trouble dealing with these issues, and Fog computing can be an acceptable solution while bringing the services closer to the end-system. Fog computing, which the main aim of Fog computing provides low latency computing services at the network edge and the reducing burden on cloud, is an enabler for MTC. Fog, also known as middleware, is required between the cloud and MTC devices. It has all been developed to address the limitations in cloud computing. In this paper, we review these recent technologies, compare their features, and is investigated the reduction of latency using Fog computing for MTCs, which is also a factor in reducing network bandwidth consumption. We formulate a model to allocate the limited processing resource of fog nodes efficiently. We appraise the performance of Fog computing using processing delay in comparison to a cloud computing approach. Simulations confirm the reduction in latency for this type of communication using Fog computing rather than cloud computing.

In recent years, the urbanization has clearly emphasized the need to pay attention to design and deployment of smart cities to reduce carbon dioxide emissions and increase energy storage. The great development of the number of vehicles on the road, along with the mismanagement of accessible parking space, has created problems about parking and increased traffic congestion in urban areas. Therefore, it is necessary to create an automatic smart parking management system that not only helps the drivers to find the appropriate parking space for their vehicles, but also reduces fuel consumption. Today, the biggest challenge is about the group of parking space on-street, which consists of two parts: identifying empty parking space in the city and proposing suitable parking space for drivers according to their criteria. The purpose of this article is to find a suitable parking space for drivers according to their specified criteria and recommend the most similar ones. When drivers plan to park on the side of the road, many criteria are considered, such as distance from the intended destination, payment, finding a parking space faster, etc. In a few articles, the issue of finding a parking space has been considered based on various criteria of drivers. In the proposed method, it is assumed that the parking spaces in the city are stored in a database and being updated constantly, Therefore, using the particle swarm optimization algorithm (PSO), drivers are offered the most suitable parking spaces according to their criteria. The implementation of this method also proved that when using PSO algorithm, although more time is spent, more requests are answered and less distance is traveled.