Pavlos I. Lazaridis

Radiometric wireless sensor network monitoring of partial discharge sources in electrical substations

A wireless sensor network (WSN) with the potential to monitor and locate partial discharge (PD) in high-voltage electricity substations using only received signal strength (RSS) is proposed. The advantages of an RSS-based operating principle over more traditional methods (e.g., time-of-arrival and time-difference-of-arrival) are described. Laboratory measurements of PD that emulate the operation of a PD WSN are presented. The hardware architecture of a prototype PD WSN is described and the particular challenges of an RSS-based location approach in an environment with an unknown, and spatially varying, path-loss index are discussed. It is concluded that an RSS-based PD WSN is a plausible solution for the monitoring of insulation integrity in electricity substations.

Creating and managing dynamic MPLS tunnel by using SDN notion

The aim of this research is using the notion of Software Defined Network (SDN) in creating and managing a Dynamic Multi-Protocol Label Switching (MPLS) tunnel in Open Shortest Path First (OSPF) network. The created tunnel has higher flexibility in terms of allocated path hops and reserved bandwidth. The path of the tunnel can be changed dynamically according to the present requirements of the network as well as its reserved bandwidth which can be changed according to the applied flow data rate. This provides faster path restoration and allows better utilization to the network resources. Moreover, it improves traffic engineering and achieves better Quality of Service (QoS) which results in more reliable network.

Comparison of Longley-Rice, ITU-R P.1546 and Hata-Davidson propagation models for DVB-T coverage prediction

This paper compares precision field-strength measurements taken by a Rohde & Schwarz FSH-3 portable spectrum analyzer with simulation results derived from the ITM coverage prediction model (Irregular Terrain Model), also known as NTIA-ITS Longley-Rice model, in conjunction with the 3-arc-second SRTM (Satellite Radar Topography Mission) geographical data, the propagation predictions of ITU-R Recommendation P. 1546 and those of the empirical Hata-Davidson model using HAAT. ITU-R P. 1546 and Hata-Davidson models exhibit higher errors at longer distances and therefore necessary corrections should be introduced in the models in order to increase propagation prediction accuracy. Especially, measurements results show that ITU-R P.1546, on average, underestimates the field strength at distances longer than 50 km. The Longley-Rice model using the terrain digital elevations is more accurate, as expected, and its results are closer to the measurement data.

Optimal Wideband LPDA Design for Efficient Multimedia Content Delivery Over Emerging Mobile Computing Systems

An optimal synthesis of a wideband log-periodic dipole array (LPDA) is introduced in this paper. The LPDA optimization is performed under several requirements concerning the standing wave ratio, the forward gain, the gain flatness, the front-to-back ratio, and the sidelobe level, over a wide frequency range. The LPDA geometry that complies with the aforementioned requirements is suitable for efficient multimedia content delivery. The optimization process is accomplished by applying a recently introduced method called invasive weed optimization (IWO). The method has already been compared to other evolutionary methods and has shown superiority in solving complex nonlinear problems in telecommunications and electromagnetics. In this paper, the IWO method has been chosen to optimize an LPDA for operation in the frequency range of 800-3300 MHz. Due to its excellent performance, the LPDA can effectively be used for multimedia content reception over future mobile computing systems.

Radiometer monitoring system for partial discharge detection in substation

Progress on the development of an insulation defect detection and location system using a partial discharge (PD) wireless sensor network (WSN) will be presented. Such a PD WSN based on intensity-only measurements has cost and scalability advantages over existing detection and location technologies based on time-difference-of-arrival measurements such as described in (I. E. Portugues, P. J. Moore, I. A. Glover, IEEE Trans. on Power Delivery, 1, 2009, pp. 20–29). Figure 1 shows a hypothetical deployment of the PD WSN in an electricity substation. The (red) pentagram denotes a PD source, yellow circles and triangles denote sensor nodes, and the yellow St Georges cross denotes the data collection/processing node. Each node of the WSN is a broadband radiometer with a measurement band of 50–800 MHz, Figure 2. Three measurement sub-bands allow the radiometer to distinguish different forms of PD; in particular internal PD and corona discharge. WirelessHart has been selected as the network communications technology since this offers improved reliability over other standards (e.g. Zigbee) in harsh industrial environments.

Comparison of contact measurement and free-space radiation measurement of partial discharge signals

Two partial discharge (PD) measurement techniques, a contact measurement technique (similar to the IEC 60270 standard measurement) and a free-space radiation (FSR) measurement technique, are compared for the case of a floating electrode PD source. The discharge pulse shapes and PD characteristics under high voltage DC conditions are obtained. A comparison shows greater similarity between the two measurements than was expected. It is inferred that the dominant mechanism in shaping the spectrum is the band-limiting effect of the radiating structure rather than band limiting by the receiving antenna. The cumulative energies of PD pulses in both frequency and time domains are also considered.

Direct and External Intensity Modulation in OFDM RoF Links

Radio-over-fiber (RoF) systems comprise light modulation and transmission of millimeter-wave signals over fiber links. The aim of this study is to investigate the performance of external and direct intensity modulation in RoF links and to analyze the drawbacks induced by different components of the optical system. In external modulation, the Mach-Zehnder modulator (MZM) is used, whereas the vertical-cavity surface-emitting laser (VCSEL) is utilized in direct modulation. Both modulation schemes are tested for a vector modulation format, i.e., the quadrature amplitude modulation (QAM), where an orthogonal frequency-division multiplexing (OFDM) scheme is used to generate signal subcarriers. The simulations are carried out with the same values of common global parameters for both schemes of intensity modulation. Although VCSEL is a promising device for future RoF systems, the external modulation shows a more robust performance compared with that of VCSEL when implemented with the OFDM modulation technique.

Optimal design of UHF TV band log-periodic antenna using invasive weed optimization

A powerful evolutionary method called Invasive Weed Optimization (IWO) is applied to achieve optimal designs of log-periodic antennas. The antennas are designed for operation in the UHF-TV band, i.e. 470-860 MHz, and are optimized with respect to the standing wave ratio (SWR), the front-to-rear (F/R) ratio, and the forward gain. The parameters under optimization are the dipole lengths, the dipole diameters, the distances between adjacent dipoles and the characteristic impedance of the transmission line that feeds the dipoles. The optimized antenna geometries that resulted from the above method seem to be significantly better than the respective ones derived from the classical design method.

Software Component Selection Based on Quality Criteria Using the Analytic Network Process

Component based software development (CBSD) endeavors to deliver cost-effective and quality software systems through the selection and integration of commercially available software components. CBSD emphasizes the design and development of software systems using preexisting components. Software component reusability is an indispensable part of component based software development life cycle (CBSDLC), which consumes a significant amount of organization’s resources, that is, time and effort. It is convenient in component based software system (CBSS) to select the most suitable and appropriate software components that provide all the required functionalities. Selecting the most appropriate components is crucial for the success of the entire system. However, decisions regarding software component reusability are often made in an ad hoc manner, which ultimately results in schedule delay and lowers the entire quality system. In this paper, we have discussed the analytic network process (ANP) method for software component selection. The methodology is explained and assessed using a real life case study.

IWO-based synthesis of log-periodic dipole array

The Invasive Weed Optimization (IWO) is an effective evolutionary and recently developed method. Due to its better performance in comparison to other well-known optimization methods, IWO has been chosen to solve many complex non-linear problems in telecommunications and electromagnetics. In the present study, the IWO is applied to optimize the geometry of a realistic log-periodic dipole array (LPDA) that operates in the frequency range 800-3300 MHz and therefore is suitable for signal reception from several RF services. The optimization is applied under specific requirements, concerning the standing wave ratio, the forward gain, the gain flatness and the side lobe level, over a wide frequency range. The optimization variables are the lengths and the radii of the dipoles, the distances between them, and the characteristic impedance of the transmission line that connects the dipoles. The optimized LPDA seems to be superior compared to the antenna derived from the practical design procedure.