Showing papers by "Vasilis Christofilakis published in 2018"

A new portable ELF Schumann resonance receiver: design and detailed analysis of the antenna and the analog front-end

Abstract: Schumann resonance oscillation detection is a complex procedure which requires customized and high-quality measurement systems. The primary objective of this work was to design and implement a stand-alone, portable, and low-cost receiver able to measure as much Schumann resonance harmonics as possible. Design, as well as detailed analysis of the efficient induction coil magnetic antenna and the low-noise amplifying-filtering chain, is presented. The detection system includes two coils back to back, resulting in a total coil length of 60 cm. The filtering and amplification chain exhibits an experimentally measured total passband gain equal to 112 dB at 10 Hz and as low as 2.88 nV/√Hz equivalent input noise. In order to validate the new portable ELF Schumann resonance detection and monitoring system, we took measurements at various spots “relatively” free from man-made electromagnetic pollution. Results have shown very clear Schumann resonance peaks for the first six modes with 10-min acquisition time.

Outage performance of mixed, parallel and serial DF relayed FSO links over weak turbulence channels with nonzero boresight pointing errors

Abstract: This work investigates the outage performance of a typical Free Space Optical (FSO) system that employs parallel decode-and-forward (DF) relay-assisted, i.e. cooperative diversity, configurations in order to combat the influence of both, atmospheric turbulence and pointing error effects. For the examined weak turbulence conditions, the irradiance fluctuations of the optical signal at the receiver is emulated through the mathematically simple and accurate gamma distribution model, while pointing error effects with nonzero boresight are modeled, in turn, through the suitable Beckmann distribution. Under these assumptions, an outage probability (OP) performance analysis is carried out, depending on the number of parallel branches and the number of DF relays in each branch. Thus, accurate and compact mathematical expressions for OP are derived, while their corresponding analytical results demonstrate concrete performance improvements, especially when the number of the connected in parallel DF relays increases. Moreover, the obtained results are verified through the corresponding simulation results.

Rainfall Measurements Due to Radio Frequency Signal Attenuation at 2 GHz

Abstract: In this paper we present an experimental validated system for measuring rainfall due to radio frequency (RF) signal attenuation at 2 GHz. Measurements took place in Ioannina, NW Greece, starting in April 2015 and lasting for twelve months. The primary acquired extensive results have shown reliable and accurate measurements for rainfall amounts smaller than 1 mm for 5 min periods. The very important innovation is that this paper presents significant earth-to-earth measurements due to rainfall attenuation (at 2 GHz) in order to act as a map for future investigation and as a prior knowledge for the behavior of other systems operating at frequencies around S-band.

Comparison of the R-R intervals in ECG and Oximeter signals to be used in complexity measures of Natural Time Analysis

Abstract: In this paper, we present a comparison of two non invasive digital systems. The one is a portable electrocardiograph (ECG) and the second a finger pulse Oximeter that was designed and assembled in our laboratory. The ultimate goal is to use a simple yet effective portable device such as an Oximeter with the prospect of calculating precisely the complexity measures of the heart rate regarding conditions leading to Sudden Cardiac Death (SCD), according to the “Natural Time Analysis (“N.T.A.”). This analysis demonstrates that when a complex system, like the human heart, approaches the critical state, it can provide us information well before the moment that the event will occur, like the case of SCD which study in this presentation.

CDMA radio on FSO links over gamma turbulence channels with nonzero boresight pointing errors

Abstract: In this work, we investigate the performance of a radio-on-free-space optical (RoFSO) communication system for transmission of CDMA signals. The optical signal propagation is affected by the combined effects of turbulence-induced fading, modelled by the gamma distribution, and the generalized nonzero boresight pointing errors. The performance assessment is implemented with the average BER metric evaluation for each user. Finally, the corresponding numerical results are presented for various parameter values concerning the CDMA wireless optical transmission.

Performance of Turbo Coded OFDM Under the Presence of Various Noise Types

Abstract: A telecommunication system uses carriers in order to transmit information through a cable or wirelessly. If each time only one carrier is transmitted, then the system s signal will not be immune to frequency selective fading. If frequency selective fading includes the working frequency of the system, then the wireless link will not be established. Orthogonal frequency division multiplexing OFDM is the primary solution for coping with inter signal interference and frequency selective fading. Many carriers can be produced by splitting a fast information stream to slower data series. Different orthogonal frequencies carry slower data series. System s performance can be further enhanced with the utilization of turbo codes. Turbo codes make the system more immune to noise effects with excellent BER results. This paper presents the thorough analysis of a turbo coded OFDM scheme using a PCCC technique in the presence of a channel which includes AWGN, phase noise, Rayleigh fading, Rician fading and Doppler shift.