No. 1 (2021)
Published:
2021-03-30
ARTICLES FROM THIS ISSUE
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Studying and Modeling the Performance of the TCM-STBC Systems in the Rayleigh Channel
Abstract
Multiple-input multiple-output (MIMO) systems will play an important role in future generations of wireless networks. Space-time block code (STBC) and space-time trellis code (STTC) are two techniques that may be used in multiantenna radio systems. This paper aims, most importantly, to study the performance of STBC systems at different values of such parameters as spectral efficiency, matrix codes and constellations. A performance comparison between STBC and STTC schemes is performed. In order to show the efficiency of the system’s ability to communicate with uncoded and coded transmission structures over AWGN and Rayleigh channels, the trellis-coded modulation (TCM) is introduced. The results obtained show that the proposed TCM-STBC system model, using one and two receiving antennas, improves the performance of Rayleigh channel communication systems at 9.5 dB and 11.5 dB for a BER of 10−5
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High-resolution Direction of Arrival Estimation Method Based on Sparse Arrays with Minimum Number of Elements
Abstract
Regular fully filled antenna arrays have been widely used in direction of arrival (DOA) estimation. However, practical implementation of these arrays is rather complex and their resolutions are limited to the beamwidth of the array pattern. Therefore, higher resolution and simpler methods are desirable. In this paper, the compressed sensing method is first applied to an initial fully filled array to randomly select the most prominent and effective elements which are used to form the sparse array. To keep the dimension of the sparse array equal to that of the fully filled array, the first and the last elements were excluded from the sparseness process. In addition, some constraints on the sparse spectrum are applied to increase estimation accuracy. The optimization problem is then solved iteratively using the iterative reweighted l1 norm. Finally, a simple searching algorithm is used to detect peaks in the spectrum solution that correspond to the directions of the arriving signals. Compared with the existing scanned beam methods, such as the minimum variance distortionless response (MVDR) technique, and with subspace approaches, such as multiple signal classification (MUSIC) and ESPIRT algorithms, the proposed sparse array method offers better performance even with a lower number of array elements and in severely noisy environments. Effectiveness of the proposed sparse array method is verified via computer simulations
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Location Estimation of Nodes in Underwater Acoustic Sensor Networks
Abstract
The paper presents a location estimation scheme for underwater acoustic sensor networks. During the first phase, the sink node begins the trapezoid formation process by activating the trapezoid formation agent. It stores relevant information in the sink’s knowledge base and in the node’s knowledge base, and also develops the search data structure required for locating the node. During the second phase, the position of the node is determined by utilizing the search data structure. Identification of the location of all nodes by traveling across the trajectory may be performed as well, as an alternative approach. When identifying the location of one node, the estimation is performed based on the search data structure. When determining the position of all nodes, the sink node agent travels along the defined trajectory and transmits beacon messages which contain the real-time location at specific points. The anchor node agent measures the signal strength and localizes itself and begins estimating the locations of other nodes within the trapezoids, using location estimation techniques. Various performance parameters are used to validate the proposed scheme
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Suboptimal Approach to Distributed Detection in Cognitive Radio Networks
Abstract
In this paper a dynamic spectrum access (DSA) concept is explored for mitigating the paucity of spectral bandwidth in cognitive radio (CR) for opportunistic, dynamic access of the spectrum without any interference. Dynamic spectrum access schemes are proposed for a distributed cognitive radio network consisting of one secondary user (SU) and many primary users (PUs). The SU has to make decisions for accessing PU channels within discrete time slots. The design of sensing and access strategies that govern channel choice in each slot for near-optimal throughput performance of the SU may be formulated as a partially observable Markov decision process (POMDP). Furthermore, it is considered that the SU incurs a cost whenever it switches to a different channel. The switching cost is expressed in terms of delay, packet loss and packet overhead. In this work, the SU access policy based on a myopic approach is proposed and evaluated
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Evaluation of Reliability of Mobile ICT Services
Abstract
This article discusses common problems with reliability and availability of ICT services, mainly in mobile networks. Internet access-related services have been examined and traditional service quality assessment methods have been compared with the proposed solutions, with the primary focus placed on availability and reliability of mobile services. The required parameter values describing reliability and quality levels have been defined and proposed
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Optimal Voting Rule and Minimization of Total Error Rate in Cooperative Spectrum Sensing for Cognitive Radio Networks
Abstract
In cognitive radio technology, spectrum sensing is essential for detecting spectrum holes which may be allotted to secondary users. In this paper, an optimal voting rule is used for cooperative spectrum sensing while minimizing the total error rate (TER). The proposed spectrum sensing method is more energy-efficient and may be implemented in practice. It is relied upon in an improved energy detector whose utilization depends on the presence or absence of the primary user. Expressions for false alarm and missed detection probabilities are derived in the paper as well. Overall performance is analyzed both for AWGN and Rayleigh fading channels, in the presence of additive white Gaussian noise (AWGN). The optimum voting rule is applied to the cooperative spectrum sensing process in order to identify the optimum number of sensing nodes and the detection threshold. Finally, an energy-efficient spectrum sensing algorithm is proposed, requiring a lower number of cognitive users for a given error bound
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FANET Drone’s 4K Data Applications, Mobility Models and Wi-Fi IEEE802.11n Standards
Abstract
With growing popularity of unmanned aerial vehicles (UAVs), the importance of flying ad-hoc networks (FANETs) is enhanced by such applications as 4K video recording, communications in search and rescue missions and goods deliveries, to name just a few. This, in turn, stimulates research on different topologies of networks existing between UAVs, with studies in this field being essential to improving performance of such networks. Several problems must be solved to effectively use UAVs in order to offer stable and reliable massive data transmission capabilities, taking into consideration quickly changing FANET topologies, types of routing, security issues, etc. In this paper, a comprehensive evaluation of FANETs used by UAVs is presented in terms of communication network challenges, data types, mobility models and standards applied in order to achieve best performance. The evaluation presented herein covers such areas as data throughput, retransmission attempts and delay
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Artificial Magnetic Conductor-based Millimeter Wave Microstrip Patch Antenna for Gain Enhancement
Abstract
In this paper, a small (20 × 20 × 2.4 mm) loaded microstrip patch antenna (MPA) with an asymmetric artificial magnetic conductor (AMC) as a ground plane is designed for millimeter wave applications. Two AMC structures are proposed; one has the property of a 0 ◦ reflection phase around 28.4 GHz, with a symmetric geometry, which makes the reflection phase insensitive to variations in both polarization and incident angle. This symmetric AMC structure ensures angular stability which is considered as a major requirement when periodic structures are used as antenna ground planes. The other structure is characterized by an asymmetric geometry and shows an interesting behavior around 28.6 GHz, where a discontinuity in the reflection phase appeared due to the fact that surface impedance nature changed from purely capacitive to purely inductive. This paper studies the effects of the two proposed AMC structures on the performance of MPAs, by using an array of 8 × 8 unit cell elements as an artificial ground plane. Simulation results show that an MPA with a symmetric AMC ground plane offers better impedance matching and a wider bandwidth. Compared with conventional MPAs, gain is enhanced and directivity is improved as well. As far as an MPA with an asymmetric AMC ground plane is concerned, its performance in terms of gain and directivity is higher than that of the conventional solution
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Orthogonal Harmonic Signals of the Generalized Class
Abstract
Telecommunications transmission technologies with OFDM rely on orthogonal harmonic signal (OHS) systems. The criteria applicable to synthesizing OHS systems of the generalized class, including both classical signals and signals whose duration exceeds the orthogonality interval, have been considered. The problems of minimizing the effective width of the spectrum of the generalized class OHS have been solved. Estimates of the efficiency of the generalized class OHS have been given
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Optimization of Gyrotron Resonator’s Dimensions
Abstract
This paper explains the procedure of determining the initial dimensions of a gyrotron resonator. In particular, the paper discusses which geometrical parameters impact the wave properties of the resonator. The solution is implemented using Matlab software and estimations are performed with the use of the SMath Studio spreadsheet
