No. 1 (2020)
Published:
2020-03-30
ARTICLES FROM THIS ISSUE
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Performance Enhancement of Coherent Optical OFDM System Using LMS Algorithm
Abstract
Instability of the local oscillator causes phase noise – a phenomenon that is a disadvantage and is considered to be a major obstacle in the functioning of coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. An attempt has been made in this paper to reduce the effects of common phase errors generated by phase noise. In this paper, a least mean square (LMS) based algorithm is proposed for estimation of phase noise. Using this proposed algorithm, the major problem of phase ambiguity caused by cycle slip is avoided and the bit error rate is greatly improved. Further, there is no requirement for modifying the frame structure of OFDM using this algorithm. A CO-OFDM system with the 8-PSK technique is used to implement the algorithm concerned. Furthermore, the algorithm, using the 8-PSK modulation technique, is analyzed and compared with the existing QPSK technique and with other algorithms. The investigations reveal that 8-PSK outperforms existing LMS algorithms using other techniques and significantly reduces the bit error rate.
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Improved Signal Detection Techniques for QOSTBC System in Fast Fading Channel
Abstract
Most existing quasi-orthogonal space time block coding (QO-STBC) schemes have been developed relying on the assumption that the channel is flat or remains static during the length of the code word symbol periods to achieve an optimal antenna diversity gain. However, in timeselective fading channels, this assumption does not hold and causes intertransmit-antenna-interferences (ITAI). Therefore, the simple pairwise maximum likelihood decoding scheme is not sufficient to recover original transmitted signals at the receiver side. To avoid the interferences, we have analyzed several signal detection schemes, namely zero forcing (ZF), two-step zero forcing (TS-ZF), minimum mean square error (MMSE), zero forcing – interference cancelation – decision feedback equalizer (ZF-IC-DFE) and minimum mean square error – interference cancelation – decision feedback equalizer (MMSE-IC-DFE). We have proposed two efficient iterative signal detection schemes, namely zero forcing – iterative interference cancelation – zero forcing – decision feedback equalization (ZF-IIC-ZF-DFE) and minimum mean square error – parallel interference cancelation – zero forcing – decision feedback equalization (MMSE-IIC-ZF-DFE). The simulation results show that these two proposed detection schemes significantly outperform all conventional methods for QOSTBC system over time selective channel.
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A Soft-Output STBC Decoder for Aeronautical Telemetry
Abstract
Alamouti encoding is a well-known space time block encoding technique used to improve the received signal quality in Rayleigh fading channels. In aeronautical telemetry, this encoding technique is applied to shaped offset quadrature phase shift keying tier generation (SOQPSK-TG) modulation in order to handle the two-antenna issue. It is provided for in telemetry-related IRIG standards. In this paper, we propose a unique decoding architecture for Alamouti-encoded SOQPSK-TG signals, taking advantage of pulse amplitude modulation decomposition with soft and hard outputs. We exploit this result to obtain a Viterbi algorithm (VA) for hard decoding and a soft output Viterbi algorithm (SOVA) for soft and hard decoding, with a twofold benefit: operation using one trellis structure, unlike decoders that are based on the 8-waveforms cross-correlated trellis-coded quadrature modulation (XTCQM) approximation, and very attractive bit error rate performance, as well as a complexity trade-off
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Analysis of Selective-Decode and Forward Relaying Protocol over κ-µ Fading Channel Distribution
Abstract
In this work, the performance of selective-decode and forward (S-DF) relay systems over κ-µ fading channel conditions is examined in terms of probability density function (PDF), system model and cumulative distribution function (CDF) of the κ-µ distributed envelope, signal-to-noise ratio and the techniques used to generate samples that rely on κ-µ distribution. Specifically, we consider a case where the sourceto-relay, relay-to-destination and source-to-destination link is subject to independent and identically distributed κ-µ fading. From the simulation results, the enhancement in the symbol error rate (SER) with a stronger line of sight (LOS) component is observed. This shows that S-DF relaying systems may perform well even in non-fading or LOS conditions. Monte Carlo simulations are conducted for various fading parameter values and the outcomes turn out to be a close match for theoretical results, which validates the derivations made
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Flow Aggregation for Energy-Aware Ad-Hoc Wireless Networks Respecting QoS Provisions
Abstract
Emerging communication technologies are now leading developers to design IT systems taking into count their energy-related considerations. Much research performed in the area of ad-hoc wireless networks tends to distribute the flows over all nodes of the network, which increases the amount of energy consumed by each node and reduces longevity of the network. To overcome these problems, this paper seeks to aggregate a set of flows within a number of nodes that is as low as possible in order to be capable of routing those flows. This proposal allows to maximize the number of network nodes that may be turned off. The proposed solution was formulated as an integer linear programming (ILP) problem using a set of energy and quality of service (QoS) constraints. This formulation minimizes the total energy consumed by the nodes to construct a topology network that is capable of meeting QoS requirement for a set flows inserted into the network. To evaluate the efficiency of the proposed model, a performance-based comparison was conducted with another routing model. The simulation results show that the proposed model offers better performance in terms of global energy consumption and network load
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A Survey on WSN and MCN Convergence Networks
Abstract
In this paper, we present a survey concerned with research focusing on the convergence of wireless sensor networks (WSN) and mobile cellular networks (MCN). The convergence of WSNs and MCNs may be a trigger stimulating new research dealing with such issues as architecture, protocols and air interfaces. The highlights and constraints of the phenomenon are discussed in this paper as well. The survey deals with convergence networks and with their smarty city applications. A few open research issues are also brought to the attention of researchers specializing in this field
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High Gain Linear 1×4 X-slotted Microstrip Patch Antenna Array for 5G Mobile Technology
Abstract
A linear 1×4 antenna array built on the Rogers RT/Duroid 5880 substrate is proposed in this paper to acquire high gain for 5G applications. The proposed design resonates at 38 GHz, i.e. in the Ka-band region, and has small patch dimensions of 5.5×2 mm. The design is simulated using CST studio. The main element consists of X-slot that provides a gain of 6.98 dB with the return loss of –24.25 dB whereas a linear array of 4 elements is made which is fed by the 50Ω m-line using the corporate feeding network which yields a gain of 13.84 dB, as well as the return loss is –15.72 dB. The centreto-centre spacing (d) of elements in the antenna array is 0.8λ
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Dual-band Bisected Psi Antenna for 3G, Wi-Fi, WLAN and Wi-MAX Applications
Abstract
This paper presents an inexpensive and simple dual-band bisected psi antenna for 3G, Wi-Fi, WLAN, and WiMAX applications is presented. The antenna comprises a bisected psi-shaped patch on a low-price FR4 substrate with a cropped ground plane on the other side, and is fed by a 50 Ω microstrip line. It operates at two distinct frequency bands of 1.87–2.76 GHz and 5.16–5.75 GHz with |S11|≤ -10 dB
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Failure Correction of a Linear Array of Coupled Parallel Vertical Dipole Antennas
Abstract
In this paper, a cuckoo search algorithm based on the combined characteristics of the brood parasite behavior and Levy flights is applied to correct the radiation pattern of a linear antenna array composed of parallel dipoles with faulty elements. An effort is made to restore the radiation pattern similar to one without any faulty elements, and the difference in the values of side lobe level and wide null depth of both patterns, as well as the voltage standing wave ratio obtained from the new voltage excitations become diminished. The examples presented in this paper show the effectiveness of this algorithm in correcting the radiation pattern of a linear array of 36 and 120 dipole antennas with four and ten failed elements, respectively. The results show that the matching condition and the wide null control produced by Cuckoo Search algorithm are more efficient in comparison with the benchmark failure correction algorithm. The approach adopted herein may be applied to other array configurations as well
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A Comparison Study of DASH Technique by Video Streaming over IP with the Use of RTP and HTTP Protocols
Abstract
Today’s Internet knows no bounds. New applications are marketed every single day. Many of them incorporate video sequences. These must be transported over the Internet quickly (often in real time). However, the Internet has not been designed for live communications and, regrettably, this may become apparent all too quickly. Countermeasures are required in the form of new, efficient transport techniques facilitating online video services. MPEG-DASH is one of such modern techniques. But how good is this new technique really? This paper delves into the matter. The paper contains an analysis of the impact that the new technology exerts on the quality of video streaming over IP networks. It also describes a new numerical tool – QoSCalc (DASH-HTTP) which has been used to analyze MPEG-DASH under different use scenarios. The results are presented graphically and their interpretation is provided
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Implementation of the Concept of a Repository for Automated Processing of Semi-Structural Data
Abstract
Semi-structural data tend to be problematic due to the sparsity of their attributes and due to the fact that, regardless of their type, they are immensely diverse. This means that data storage is a challenge, especially when the data contained within a relational database – often a strict requirement defined in advance. In this paper, we present a thoroughly described concept of a repository that is capable of storing and processing semi-structural data. Based on this concept, we establish a database model comprising the architecture and the tools needed to search the data and build relevant processors. The processor described may assign roles and dispatch tasks between the users. We demonstrate how the capacities of this repository are capable of overcoming current limitations by creating a system for facilitated digitization of scientific resources. In addition, we show that the repository in question is suitable for general use, and, as such, may be adapted to any domains in which semi-structural data are processed, without any additional work required
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Two Extensions of Trust Management Languages
Abstract
This article is focused on the family of role-based trust management languages (RT). Trust management languages are a useful method of representing security credentials and policies in large distributed access control mechanisms. They provide sets of credentials that are assigned to individual roles performed by the specific entities. These credentials provide relevant information about security policies issued by trusted authorities and define user permissions. RT languages describe the individual entities and the roles that these entities play in a given environment. A set of credentials representing a given security policy defines which entity has the necessary rights to access a specific resource and which entity does not have such rights. This study presents the results of research focusing on the potential of the family of RT languages. Its purpose is to show how security policies may be applied more widely by applying an inference system, and then using the extensions of the credentials, by taking into account time-related information or the conditions imposed with regard to the validity of such credentials. Each of these extensions can be used jointly or separately, offering even a wider range of opportunities
