University of Ioannina Department of Physics Electronics Telecom. & App. Laboratory Panepistimioupoli, Ioannina GR-45110, GREECE (Ph.D. Candidate)
Technological Educational Institute of Epirus Department of Informatics and Telecom. Microelectronics & Telecom. Laboratory Kostakioi, Arta GR-47100, GREECE (Lab Professor)
Spyridon K. Chronopoulos was born in Athens, Greece. He received the B.Sc. degree in Physics from the University of Ioannina, Greece and the M.Sc. degree in “Modern Electronic Technologies” from the same University. He is, currently, a Ph.D. candidate at Electronics, Telecommunications and Applications Laboratory of Physics Department in University of Ioannina, Greece. He is also a member of the Microelectronics and Telecommunications Research Laboratory of Technological Educational Institute of Epirus, Arta, Greece. His current research interests are in the area of Electronics and Telecommunications with particular focus on mobile communications, communication services, antenna design, wireless transceiver design, hardware implementations and satellite communication systems.
Abstract: Orthogonal frequency division multiplexing (OFDM) is vastly used in wireless networks. Its superiority relies on the fact that information can be split in large amount of frequencies. Each frequency is called information subcarrier. OFDM exhibits excellent annotation in channel fades and interferers as only a few subcarriers can be affected and consequently a small part of the original data stream can be lost. Orthogonality between frequencies ensures better spectrum management and obviates the danger of intersymbol interference. However, an essential problem exists. OFDM systems have high peak to average power ratio. This implies large fluctuations in signal power, ending up in increasing complexity of ADCs and DACs. Also, power amplifiers must work in a larger linear dynamic region. In this paper we present two new techniques for reducing Peak to Average Power Ratio (PAPR), that can be added in any OFDM system and we compare them with other existing schemes.
Notes: The research Project is co-funded by the European Union â European Social Fund (ESF) & National Sources, in the framework of the program âHRAKLEITOS IIâ of the âOperational Program Education and Life Long Learningâ of the Hellenic Ministry of Education, Life Long Learning and religious affairs.
Abstract: In this paper we investigate real-time satellite communications through the evaluation of satellite coverage over Ioannina Airport in Greece for the purpose of generalizing the introduced method for selected areas on the surface of the Earth. The necessary simulation is performed using AGI's STK suite. This tool is available for all types of vehicles, facilities, targets and sensors. Specifically it is possible the calculation of single-object coverage to track the position of a vehicle or facility along Ioannina Airport in Greece. The survey describes the conclusions coming from the study of coverage on the airport of Ioannina not only from GPS satellites but also from other satellite categories specialized for civilian communications, military and science operations. Additionally new parameter values involving propagator issues of satellites are suggested taking into consideration the maximum coverage coming from the satellites that have been studied and belong to a large number of different categories.
Abstract: Galileo is the program that has been launched by the European Union for the purpose of building a Global Navigation Satellite System (GNSS) for serving civilians and to exist under civil control. Our project combines many previous researched scenarios for Galileo system to a final one, which has been simulated and adjusted to meet the most demanding standards (of proposed GNSS services). The final simulated scenario is consisted of 30 (27+3 spare) satellites allocated in 3 orbital planes.
Abstract: This paper presents design issues of a dipole antenna for wireless communications which is printed on a dielectric substrate and fed by a microstrip line. A discontinuity in form of a rightâangle bend close to the gap of the dipole strips provides a crucial parameter for discussion. The impact of mitering these bends in return loss, resonance bandwidth and radiation pattern of antenna has been investigated. Both simulated and experimental results propose this observation.
Abstract: Multipleâoutput transmitter implementation based on Direct Digital Synthesis (DDS) architecture is presented and investigated. A particular number of identical and independent units compose the proposed device. DDS technology is applied on the first stage of these units and provides amplitude, phase and frequency adjustments on the corresponding output signals. Quadrature mixers are driven by DDS's outputs and corresponding amplification and filtering circuits are also used to prepare the radiofrequency signals in the outputs of the proposed device. Design issues of analog circuitry and digital control logic are also described. Phase, amplitude and frequency accuracy that DDS technology provides are further discussed. Experimental results indicate that the proposed transmitter architecture can provide independent RF signals for wireless applications.
Abstract: This paper describes the design and implementation of an UWB Impulse Radio transmitter. This UWB transmitter produces very short pulses with possibility of time-shifting to be used in cases of Pulse Position Modulation (PPM). The transmitter, which is based on step recovery diode (SRD), can operate at 50 Mbps with high repetition rate. Experimental results show that, ultra short pulses with duration of about 1nsec and spectrum exceeding 2 GHz at â10 dB, are produced and transmitted.
Abstract: UWB communications have attracted considerable interest, targeting applications in high-speed data transfer wireless communication systems. This paper studies the effects of matched filter receiver in the performance of such a system. Such effects are evaluated in terms of the Bit Error Rate (BER) for a Binary Pulse Position Modulation (BPPM) scheme, considering multipath propagation channel and the presence of noise. The case of imperfect channel estimation is taken into account. Dependence of BER on parameters such as signal to noise ratio, number of estimation pulses and correletor taps is also presented.
Abstract: Latest technologies in wireless communications present new challenges on antenna design. Reduced size antennas with self reconfigurable ability are characteristical of smart antennas. This paper presents the practical implementation issues of making an automatic smart antenna tuning system varying the resonant frequency of the antenna using a varactor. The primary parameter for changing varactor's value is antenna's VSWR which is monitored by a uC. Additionally, the uC also controls the varactor's value.
Abstract: In modern mobile communication system, low profile antennas capable of broadband operation are required. Nevertheless there is a problem in changing fast and easy the resonant frequency to achieve effective bandwidth. In this paper we examine in particular how an added capacitive load affects the resonant frequency, the VSWR and the current distribution of a Planar antenna. The resonant frequency dependence from the capacitance load is useful parameter for making full self-tuning antennas.
Abstract: Orthogonal frequency division multiplexing (OFDM) is a multicarrier data transmission, where a single stream of information is divided over a large number of subcarriers. The primary purpose of this work was to find out the relationships connecting BER performance in noisy environments and the number of transmitted subcarriers. In order to simulate this kind of environment, various noise types where taken into consideration such as complex Rayleigh fading, complex rician noise, AWGN and phase noise.
Abstract: In this paper we investigate the performance of IEEE 802.16-2005 OFDMA system with high order QAM/QPSK mapping in the presence of high SNR values that are found both in Urban and Rural Environments. We consider OFDMA scheme with an AWGN channel and analyze their performance in terms of the BER in the system.
Abstract: In this paper, we constructed a scenario, using AGI's Satellite Toolkit, simulating a Geostationary Satellite and several Base Stations. The purpose was to measure and investigate the reliability of such a satellite system for data rates up to 1000 Mbps. The satellite transmitter used QPSK modulation and a multibeam antenna for accomplishing real-time satellite access and coverage over the various facilities under test. Also the validation of the certain system was performed under rain conditions, taking into consideration the need of QoS, giving results for the needed hardware to be implemented in a future construction. This system can be a part of a larger communication system involving 3G/4G, VoIP and multimedia services.
Abstract: In this paper we demonstrate the evaluation of the quality of satellite coverage over Ioannina Airport and consequently to various areas and objects on the surface of Earth. The necessary simulation is performed using AGIâs STK suite. This tool is available for all types of vehicles, facilities, targets and sensors. Specifically it is possible the calculation of single-object coverage to track the position of a vehicle or facility along Ioannina Airport in Greece. The survey describes the conclusions coming from the study of coverage on the airport of Ioannina not only from GPS satellites but also from other satellite categories specialized for civilian communications, military and science operations. Additionally new parameter values involving propagator issues of satellites are suggested taking into consideration the maximum coverage coming from the satellites that have been studied and belong to a large number of different categories.
