No. 2 (2020)
Published:
2020-06-30
ARTICLES FROM THIS ISSUE
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A Study of Wireless Sensor Networks to Comprehend their Relevance to Different Applications
Abstract
Wireless sensor networks (WSNs) have experienced enormous growth, both in terms of the technology used and their practical applications. In order to understand the features of WSNs that make the solution suitable for a specific purpose, one needs to be aware of the theoretical concepts behind and technological aspects of WSNs. In this paper, the significance of WSNs is illustrated, with a particular emphasis placed on their demands and on understanding researchrelated problems. A review of the literature available is presented as well. Detailed discussions concerning sensor node architecture, different types of sensors used and their relevance for various types of WSNs is presented, highlighting the need to achieve application-specific requirements without degrading service quality. Multipath and cluster-based routing protocols are compared in order to analyze QoS requirements they are capable of satisfying, and their suitability for different application areas is reviewed. This survey highlights the performance of different routing protocols, therefore providing guidelines enabling each of the routing techniques to be used, in an efficient manner, with factors such as specific network structure, protocol operation and routing path construction taken into consideration in order to achieve better performance
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Simulations of the MAC Layer in the LoRaWAN Networks
Abstract
The Internet of Things is changing the approach to data transmission, protocol design and network services. The challenge faced by designers of IoT solutions is to determine the scalability of a given technology, with a particular emphasis placed on unlicensed frequency bandwidth (ISM) transmission in highly urbanized areas. Because the design and implementation of a wireless network for the Internet of Things, relying on each of the presented technologies, is expensive and time consuming, it must be preceded by a performance assessment based on computer simulations. The literature contains various approaches to modeling the mechanisms of the MAC layer of LoRa technology and to its implementation in LoRaWAN networks. The article provides an overview of major LoRa MAC network simulators. It presents and comments on the most important research results obtained by the authors of the aforementioned software
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Estimation of UFMC Fading Channels Using H∞ Filter
Abstract
Universal filtered multi-carrier (UFMC) modulation is a very powerful candidate to be employed for future 5G mobile systems. It overcomes the limitations and restrictions in current modulation techniques employed in 4G mobile systems and supports future applications, such as machineto-machine (M2M), device-to-device (D2D), and vehicle-tovehicle (V2V) communications. In this paper, we address the estimation of UFMC fading channels based on the comb-type pilot arrangement in the frequency domain. The basic solution is to estimate the fading channel based on the mean square error (MSE) or least square (LS) criteria with adaptive implementation using least mean square (LMS) or recursive least square (RLS) algorithms. However, these adaptive filters seem not to be effective, as they cannot fully exploit fading channel statistics, particularly at high Doppler rates. To take advantage of these statistics, time-variations of the fading channel are modeled by an autoregressive process (AR), and are tracked by an H∞ filter. This, however, requires that AR model parameters be known, which are estimated by solving the Yule-Walker equation (YWE), based on the Bessel autocorrelation function (ACF) of the fading channel with a known Doppler rate. Results of Matlab simulations show that the proposed H∞ filter-based channel estimator is more effective when compared with existing estimators
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First and Second Order Characteristics of a Wireless Three-hop Relay Channel with the Presence of Rayleigh Fading
Abstract
In this paper, a wireless three-hop relay communication system operating in a Rayleigh multipath fading environment is analyzed. The output signal from such a system is a product of signal envelopes from all sections, meaning that it is actually a product of three random variables (RVs) with Rayleigh distribution. We considered here the first-order characteristics: probability density function (PDF), cumulative distribution function and outage probability (OP). Then, the moments and amount of fading (AoF) were derived in the closed forms. The second order characteristics we present include the following: level crossing rate (LCR) and average fade duration (AFD). A few graphs are given to show the impact of the specific parameters of the wireless three-hop relay system
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Extrapolation of Electromagnetic Response from Linear Antennas in Time Domain without Late-Time Instabilities in Numerical Solution of EFI Equation
Abstract
The paper presents a new hybrid method relied upon to solve integral equations of the electric field in time domain and to model linear antennas with pulse excitation. The method consists in a mixed, numerical-analytical description of the process that helps maintain the stability of calculations during the late time phase. As described in the analytical part, the modified spherical Bessel function of the first kind allows for extrapolation with a high degree of accuracy and loworder expressions. The modified spherical Bessel functions of the first kind are of the oscillating character, and their combination with the exponential factor makes them convenient for extrapolation of the answer of the antenna with pulse excitation. New functions are introduced to computational practice
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Performance Evaluation of the Threshold Call Admission Policy in Multi-rate Loss Systems
Abstract
In this paper we consider a link, characterized by specific capacity, that services multi-rate random or quasirandom traffic. Random traffic is generated by an infinite number of traffic sources, while quasi-random traffic is generated by a finite population of traffic sources. The link is modeled as a multi-rate loss system. Handover and new calls are distinguished. New calls compete for the available bandwidth under a threshold call admission policy. In that policy, a new call of a particular service-class is not allowed to enter the system if the in-service handover and new calls of the same service-class plus the new call, exceed a predefined threshold (which can be different for each service-class). On the other hand, handover calls compete for the available bandwidth based on the complete sharing policy. We show that the steady state probabilities in the proposed models have a product form solution (PFS). The PFS leads to a convolution algorithm for accurate calculation of congestion probabilities and link utilization
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Performance Evaluation of Two-Link Multirate Loss Models with Restricted Accessibility
Abstract
We consider a two-link communication system with restricted accessibility that services Poisson arriving calls of many service-classes and propose a multirate teletraffic loss model for its analysis. In a restricted accessibility system, call blocking occurs even if available resources do exist at the time of a call’s arrival. In the two-link system under consideration, each link has two thresholds (offloading and support) which express the in-service calls in a link. The offloading threshold represents the point from which a link offloads calls. The support threshold (which is lower than the offloading threshold) defines the point up to which a link supports offloaded calls. The two-link system with restricted accessibility is modeled as a loss system whose steady state probabilities do not have a product form solution. However, approximate formulas for the determination of call blocking probabilities are proposed. In addition, we also provide a corresponding analysis related to the case of quasi-random traffic (i.e. traffic generated by a finite number of users). The accuracy of all formulas is verified through simulation and is found to be quite satisfactory
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Modeling of Complex Non-Full-Availability Systems
Abstract
This article presents an analytical model of complex non-full-availability telecommunications systems. The high degree of accuracy of the model is demonstrated by a comparison with the results of simulation experiments. Due to the introduction of an availability parameter, this model may be used in the future for analyzing real systems, such as, for example, cloud computing infrastructure. This will be possible provided that the function combining the physical structure of the system and the availability parameter is specified. This problem will be addressed in our future work and will constitute the next stage of research undertaken by the authors
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V2X Communications for Platooning: Sensor Inaccuracy Aspects
Abstract
Platooning is a future approach to autonomous driving in which vehicle-to-vehicle and vehicle-to-infrastructure communications play an important role. Tests performed in the past showed that a significant reduction in fuel consumption is possible when cars are traveling in a dense platoon formation. To increase the level of their awareness of the surrounding objects and to maintain a very short distance to the preceding vehicle, highly reliable on-board sensors are required. This paper discusses the impact of sensor inaccuracy on the performance and behavior of and autonomous vehicle platoon that makes use of wireless communications supported by context information from various databases and maps
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An Expert System for Automatic Classification of Sound Signals
Abstract
In this paper, we present the results of research focusing on methods for recognition/classification of audio signals. We consider the results of the research project to serve as a basis for the main module of a hybrid expert system currently under development. In our earlier studies, we conducted research on the effectiveness of three classifiers: fuzzy classifier, neural classifier and WEKA system for reference data. In this project, a particular emphasis was placed on fine-tuning the fuzzy classifier model and on identifying neural classifier applications, taking into account new neural networks that we have not studied so far in connection with sounds classification methods
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Retransmission as a Replacement Forward Error Correction in Noiseless LV Networks used for Narrowband PLC
Abstract
The article describes a project concerned with deploying PLC technology in railway light signals. The proposal increases reliability of communication between railway light signals and the railway automation center, relying on frame retransmissions instead of the FEC technique. The paper presents the results of long-term FER measurements performed in a narrowband PLC-based communication system. The said results are used as communication reliability metrics. Deployment of dual channels in order to increase communication reliability is discussed as well, as is efficiency of FEC-based convolutional coding. The results are verified in a real world environment
