Journal of Communication Engineering
Volume:10 Issue: 1, Winter-Spring 2021

Orthogonal frequency division multiplexing (OFDM) is an attractive approach for multi-channel transmission. Due to some advantages such as high spectral efficiency, simplicity in channel equalization, and robustness to the fading channel, the OFDM technique has been generally used in many wireless communication devices. Besides these advantages, the OFDM systems usually experience a high peak-to-average power ratio (PAPR). As a result of the high PAPR, the OFDM signal is clipped during the passing via a non-linear power amplifier. The precoding techniques decrease the autocorrelation of the input data symbols to mitigate the high PAPR. In this paper, we compare WHMT, VLMT, DCMT, DHMT, DFMT, ZCMT, and CVMT precoding approaches in terms of autocorrelation and PAPR reduction performance. We demonstrate that the serial combinations of both ZCMT and CVMT precoding matrices with the IFFT matrix cancel the impact of each other when their dimensions are the same. In this case, a sparse matrix is produced and hence the PAPR of the OFDM signal is remarkably reduced. This issue is proved by the mathematical calculations and verified by the simulation results. It is also presented that DFMT, ZCMT, and CVMT precoding schemes have almost the same PAPR reduction performance and they are the best among their counterparts.

In this research, performance analysis for the composition of non-orthogonal and orthogonal cellular digital television broadcasting is investigated. A downlink multi-carrier layered division multiplexing (LDM) superimposed with an evolved multimedia broadcast multicast service (eMBMS). We define two broadcast service providers (BSP), which offer different radio access technology (RAT). The BER and Sum-Rate efficiency are selected as our criteria. The proposed downlink composition framework can work without a subscriber identity module (SIM card) uplink and internet protocol (IP). Mathematical analysis, based on the exact closed-form expressions, is consistent with the theory of the proposed composition LDM/eMBMS. Evaluation and performance are done based on the Monte Carlo iterative methodology. The results show that the BER and Sum-Rate performance of a composition framework outperforms compared with LDM/eMBMS individually system.

In this study, we present a comprehensive overview of the exact and approximate models and methods that are available to measure the dispersion of random rough surfaces. We investigated the structural implementation of such surfaces in the finite-difference time-domain (FDTD) simulation environment and introduced a method for error reduction in simulated environments with such surfaces to improve the accuracy of near-path scattering of random rough surfaces. For this aim, a new adsorbent consisting of two types of adsorbents with distinct properties is proposed. During different tests in environments with the random rough surfaces and more complex environments with abnormal dispersers, the superiority, and higher performance of the proposed adsorbents are verified and then, properties of the adsorbents are investigated. Next, two dimensional random rough surfaces are analyzed to investigate electromagnetic scattering. To determine the electromagnetic scattering field, surface height's and slope's joint probability density function is calculated and utilized after generating a two-dimensional rough surface. The ray-tracing base model is exploited, and then the Monte-Carlo technique is hired to convert an infinite integration form into the form of finite integration.

In this paper, 2D-FDFD method is applied for measuring electrical properties of dielectric materials using an open-ended coaxial probe. A SMA connector with flange is used as the coaxial probe and the reflection coefficient from probe aperture in contact with dielectric is measured by a vector network analyzer. To convert the aperture-plane reflection coefficient to dielectric permittivity, first, the coaxial probe is modeled by the 2D-FDFD method and then the genetic algorithm is employed to solve the inverse problem. The accuracy of the proposed method is investigated by measuring the dielectric properties of three known materials. The mean absolute percentage errors are below 10% and the maximum absolute percentage error is below 12%. Thus, good agreement between measured and actual values are observed.

Explicit and hybrid equivalent models of bulk current injection probe are reviewed, these models don’t take slot and ferrite dielectric constant capacitive effects into account, which caused the appearance of negative values in the real part of ferrite permeability spectra when extracting it from measured input impedance of the probe. In this paper, these capacitances are calculated using CST Electrostatic Solver, then its effect on the probe equivalent series impedance, voltage transfer ratio, and the core predicted permeability are evaluated. The evaluation shows that introducing these capacitances cancels the abnormal negative permeability resulting in the model, without affecting the model validation.

In communication systems, Low-Noise Amplifiers (LNAs) with low noise performance are essential components. This work introduces a LNA for radio frequency front-end receivers with a frequency range of 8–9.6 GHz. The planned LNA contains a two-stage high-electron-mobility transistor cascade amplifier with a minimum measured Noise Figure (NF) of 0.8 dB and a peak gain of 25 dB at room temperature. The proposed LNA is based on a GaAs FET transistor (CE3512K2) because of its good low noise performance at microwave frequency bands. The measured results demonstrate that the proposed LNA is perfectly matched over the whole operational frequency spectrum of the input/output ports (|S11| < -10 dB, |S22| <-10 dB). In addition, the suggested LNA draws a current of 20 mA and operates with a +3.6 V and a -3.6 V power supply. The recommended LNA is appropriate for X frequency bands applications.

Sea target detection in the HSP-FLSAR images has not been addressed so far in the literature. In this paper we carry out a comparative evaluation of existing SAR target detection algorithms in the case of monostatic HSP-FLSAR range Doppler images assuming a platform diving trajectory. To do so, various CFAR methods, including CA-CFAR, SOCA-CFAR, GOCA-CFAR, OS-CFAR, VIE-CFAR, and G0 distribution CFAR algorithms, are used to detect a set of point scatterers in simulated images. The performance of methods is compared based on receiver operating characteristic curves. Simulation results show that OS-CFAR has the best probability of detection for a fixed probability of false alarm. This paper can be a starting point to find better target detection methods in HSP-FLSAR images.

We study through a drywall imaging using synthetic aperture radar (SAR) method. Transmission and reflection characteristics of the wall are analyzed by a rigorous coupled-wave analysis (RCWA) method. The Bragg modes are investigated on analytic formulation and reconstructed image. The cutoff frequency for different Bragg modes is calculated and the relative power carried by each of these modes is shown. The Green function of such a periodic structure is derived by representing a line source radiation in the spectral domain. The analytical results are then validated by the numerical FEM results using the COMSOL software and the effect of the number of the Bragg modes is shown. Having numerically calculated backscattered fields of a target behind the wall and the free-space Green function, the SAR image of the target is computed and the image artifacts due to the presence of the wall are addressed. Firstly, we show that the target image is still distorted and not focused even with the background subtraction. Secondly, by properly employing the phase of the wall Green function instead of the free-space Green function, we indicate that the target image is successfully refocused.

One of the most critical challenges of wireless sensor networks is the limited energy of the nodes, which has tried to manage energy consumption in these networks by using more accurate clustering. So far, many methods have been proposed to increase the accuracy of clustering, which reduces the energy consumption of nodes and thus increases network throughput. In this paper, we propose a method for clustering wireless sensor networks using the whale optimization algorithm, which results in increased throughput in these networks. Although much work has been done in this area in terms of energy, some do not have good throughput. Therefore, in this paper, a clustering method based on the whale optimization algorithm is proposed. Features of this algorithm include easy implementation, providing high- quality solutions, quick convergence, and the ability to escape from local minima. Also, in terms of clustering, in addition to paying attention to energy consumption, has appropriate throughput. In the proposed method, the Euclidean distance is used to assign data to the cluster and determine the cluster centers by the whale optimization algorithm. In other words, concentrated clusters are created. Then, according to the two remaining energy parameters and the distance of the nodes to the centers of the cluster, two clusters are selected. To evaluate the research, we have used MATLAB software and compared the proposed method with one of the latest works. The results show an improvement in throughput and comparable in terms of energy

Recently proposed distributed incremental fractional tap-length (FT) variable-length least mean square (LMS) technique do not consider noisy links errors, which occur during the communication of local estimations between nodes. In this paper, we study the noisy links effect on the performance of this algorithm. We derive a mathematical formulation for the steady-state length at each node. Our derived relationship shows how steady-state tap-length is affected by noisy links. Simulations confirm that there is a good match between the theory and simulated tap-length. Furthermore, the critical result is that, as the noise level increases, the steady-state tap-length decreases compared to the ideal link version. However, in low noise conditions, this length is still larger than the optimal filter length.

localization plays a significant role in lots of underwater applications. Underwater communications encounter critical challenges different from terrestrial wireless sensor networks. In this study, we focus on the challenges of the variable sound speed underwater and synchronization. Among localization approaches, the received signal strength (RSS) is cost-effective and, unlike time-based approaches is synchronization-free. In some applications, the source transmitted power is unknown or hard to obtain. While this parameter is required to be known in RSS-based approaches, it is not a requirement in differential RSS (DRSS) based approaches. Regarding these issues, in this paper, we propose a DRSS-based localization algorithm considering an iso-gradient sound speed profile in an underwater medium when the source transmitted power is unknown. To improve the received signals’ SNR, we use a network of sensor arrays where beamforming is conducted within each array. Then, DRSS values are calculated and the iterative DRSS-based localization algorithm is presented. We show the effectiveness of the proposed algorithm compared with the Array-RSS and the Array-TDOA algorithms via computer simulations. Results indicate that the Array-DRSS performs accurately when the source transmitted power is unknown. Moreover, it outperforms the Array-TDOA algorithm when low bandwidth is available.

In this paper, an iterative algorithm for direction of arrival (DoA) estimation of coherent sources with a uniform circular array (UCA) is proposed. There is an additional error in the DoA estimationof signals after mapping UCA to virtual uniform linear array (VULA), due to approximation of beamspace transformation. This error depends on the direction of emitters. In the proposed algorithm, the dominant term of error is reduced using two beamformers. Then, the DoA of coherent sources are estimated by construction of Toeplitz covariance matrix and using the MUSIC algorithm. The processes of DoA estimation and reduction of the approximation error are doneiteratively. Also, an analytical expression is derived for the approximation of bias for DoA estimation of coherent sources. Simulation results show that the proposed algorithm has a better performance in comparison to the conventional methods.