No. 1 (2014)
Published:
2014-03-30
ARTICLES FROM THIS ISSUE
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Burst Ratio in Concatenated Markov-based Channels
Abstract
This paper deals with the burst ratio parameter, which describes the burstiness of a packet loss observed in digital networks. It is one of the input parameters of E-model – the most widely used method of assessing conversational quality of telephony. The burst ratio is defined for one channel scenario so it can be calculated when the whole transmission path has been characterized by a single set of parameters. The main objective of the paper is to extend the burst ratio definition when the transmission path is defined as a tandem concatenation of transmission channels being described by their individual burst ratios. It is assumed that packet loss of a single channel is described by a 2-state Markov chain. The final result of the research is an equation describing the burst ratio parameter when the transmission path consists of multiple concatenated channels. The derived formula has been validated by extensive simulations.
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New Tool for Examining QoS in the VToIP Service
Abstract
This paper is dedicated to the subject of measuring QoS in the Video Telephony over IP (VToIP) service. QoS measurement models in general and then models designed specifically for measuring QoS in the VToIP service are presented. A new numerical tool for examining the quality of VToIP video streams VToIP is described. The tool’s functionality is then put to the test in a number of analysis scenarios. The results and insights gained from the analyses are then presented in several diagrams, and interpreted. The paper concludes with a summary and an outlook on further areas of work.
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Analysis of Content Quality Evaluation within 3DTV Service Distribution Systems
Abstract
In the following paper, evaluation of quality of content distributed within 3DTV service is assessed. The performed analysis reveals a multiplicity of parameters as a compound factor defining the contemporary approach towards quality assessment. Taking into consideration a successful telecommunication service creation, an examination of content chain identifies crucial stages founding the path of modern services of stereoscopic content distribution quality evaluation.
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Quality of Variable Bitrate HD Video Transmission in New Generation Access Network
Abstract
Article presents influence of multiplying variable bitrate high definition (HD) video streams in an access network link on Quality of Service (QoS). The aim of a conducted study is to define key parameters influencing Quality of Experience (QoE). Numerous simulations were performed and indicators like packet loss, delay, jitter, frame loss and bandwidth utilization were observed. Moreover, two independent algorithms were used to indicate QoE values of video streams. These are SwissQual VQuadHD and Telchemy VQMon applications which provided credible full reference and no reference algorithms, respectively. In the article evaluation of accuracy of no reference algorithm is performed. In future work it is planned to build analytic model of VBR video transmission and to undertake more thorough research of transmitting multiplied HD video streams in an access network using various QoS policies and optimizing size of buffers.
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Videotoms in Objective and Subjective Quality Tests of Video
Abstract
This paper proposes idea of videotoms usage in quality tests of video signals. This concept simplifies parametric model creation for television services such as IPTV (Internet Protocol Television), VoD (Video on Demand) and others. Videotom is simple, well-defined video sequence in the context of video quality tests. Presented idea was used in both objective and subjective tests of influence selected network parameters: jitter of delay, packet loss and packet corrupt on the video quality measured using Mean Square Error ( MSE ) and Mean Opinion Score (MOS) metrics. Results showed that proposed method is useful especially for subjective tests and it can reduce costs and time for them.
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Gradient-Based Algorithms in the Brachistochrone Problem Having a Black-Box Represented Mathematical Model
Abstract
Trajectory optimization problems with black-box represented objective functions are often solved with the use of some meta-heuristic algorithms. The aim of this paper is to show that gradient-based algorithms, when applied correctly, can be effective for such problems as well. One of the key aspects of successful application is choosing, in the search space, a basis appropriate for the problem. In an experiment to demonstrate this, three simple adaptations of gradient-based algorithms were executed in the forty-dimensional search space to solve the brachistochrone problem having a blackbox represented mathematical model. This experiment was repeated for two different bases spanning the search space. The best of the algorithms, despite its very basic implementation, needed only about 100 iterations to find very accurate solutions. 100 iterations means about 2000 objective functional evaluations (simulations). This corresponds to about 20 iterations of a typical evolutionary algorithm, e.g. ES(µ,,,λ).
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Comparative Study between Several Direction of Arrival Estimation Methods
Abstract
In this paper a comparative study, restricted to one-dimensional stationary case, between several Direction of Arrival (DOA) estimation algorithms of narrowband signals is presented. The informative signals are corrupted by an Additive White Gaussian Noise (AWGN), to show the performance of each method by applying directly the algorithms without pre-processing techniques such as forward-backward averaging or spatial smoothing.
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Transmit Diversity in the Downlink for the TETRA-TEDS System
Abstract
In the paper a proposal for the improvement of performance for the TETRA Enhanced Data System (TEDS) employing transmit diversity based on two antennas in the downlink is described. The key idea of the considerations relies on using the space-frequency coding algorithm. The proposal described required some relatively simple changes to the existing TEDS’s Single Input Single Output (SISO) interface but the original number of payload and signaling symbols in the normal downlink burst is preserved. The simulation results obtained indicate a significant improvement in performance. The Eb/No parameter could be reduced from 5 to 8 dB with respect to Frame Error Rate (FER), compared to a single antenna transmission for the same FER = 10−3.
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Normalized Gaussian Approach to Statistical Modeling of OFDM Signals
Abstract
This article concerns modeling of statistical properties of OFDM signals with the help of “normalized Gaussian” model, proposed by Kotzer et al. In this paper there is provided an extended formulation of the model, supplemented by an expression for probability density, extending possible applications of the model in theoretical works. Numerical results for verification of the model are provided and a more accurate alternative is suggested.
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Subcarrier Gain Based Power Allocation in Multicarrier Systems
Abstract
The Orthogonal Frequency Division Multiplexing (OFDM) transmission is the optimum version of the multicarrier transmission scheme, which has the capability to achieve high data rate. The key issue of OFDM system is the allocation of bits and power over a number of subcarriers. In this paper, a new power allocation algorithm based on subcarrier gain is proposed to maximize the bit rate. For OFDM systems, the Subcarrier Gain Based Power Allocation (SGPA) algorithm is addressed and compared with the standard Greedy Power Allocation (GPA). The authors demonstrate by analysis and simulation that the proposed algorithm reduces the computational complexity and achieves a near optimal performance in maximizing the bit rate over a number of subcarrier.
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Gyrotron Technology
Abstract
The article presents a microwave vacuum tube called gyrotron. Its applications, construction and principle of operation are briefly described. It is also discussed the issue of an appropriate electron beam generation and formation.
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An Ontological Framework for Representing Clinical Knowledge in Decision Support Systems
Abstract
In the last decades, clinical evidence and expert consensus have been encoded into advanced Decision Support Systems (DSSs) in order to promote a better integration into the clinical workflow and facilitate the automatic provision of patient specific advice at the time and place where decisions are made. However, clinical knowledge, typically expressed as unstructured and free text guidelines, requires to be encoded into a computer interpretable form suitable for being interpreted and processed by DSSs. For this reason, this paper proposes an ontological framework, which enables the encoding of clinical guidelines from text to a formal representation, in order to allow querying, advanced reasoning and management in a well defined and rigorous way. In particular, it jointly manages declarative and procedural aspects of a standards based verifiable guideline model, named GLM-CDS (GuideLine Model for Clinical Decision Support), and expresses reasoning tasks that exploit such a represented knowledge in order to formalize integrity constraints, business rules and complex inference rules.
