Spyridon K. Chronopoulos

Enhanced PAPR in OFDM without Deteriorating BER Performance

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.

Voice Handicap Index and Interpretation of the Cutoff Points Using Receiver Operating Characteristic Curve as Screening for Young Adult Female Smokers

The relationship between smoking and alterations of the vocal tract and larynx is well known. This pathology leads to the degradation of voice performance in daily living. Multiple assessment methods of vocal tract and larynx have been developed, and in recent years they were enriched with self-reported questionnaires such as Voice Handicap Index (VHI). This study determined the cutoff points of VHIs total score and its three domains for young female smokers in Greece. These estimated cutoff points could be used by voice specialists as an indicator for further clinical evaluation (foreseeing a potential risk of developing a vocal symptom because of smoking habits). A sample of 120 female nondysphonic smokers (aged 18-31) was recruited. Participants filled out the VHI and Voice Evaluation Form. VHIs cutoff point of total score was calculated at the value of 19.50 (sensitivity: 0.780, 1-specificity: 0.133). Specifically, the construct domain of functional was 7.50 (sensitivity: 0.900, 1-specificity: 0.217), for physical it was 8.50 (sensitivity: 0.867, 1-specificity: 0.483), and for emotional it was 7.50 (sensitivity: 0.833, 1-specificity: 0.200) through the use of receiver operating characteristic. Furthermore, VHI could be used as a monitoring tool for smokers and as a feedback for smoking cessation.

Satellite multibeam signaling for multimedia services

In this paper, we constructed a scenario, using AGIs 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.

System Performance of an LTE MIMO Downlink in Various Fading Environments

This article presents simulation results for a realistic implementation of the downlink MIMO LTE Release 8 standard in fading environments. A 4x2 MIMO Channel configuration has been used as a basis in the simulation scenarios and various key characteristics of the MIMO channel and the LTE radio interface, including physical layer and radio resource management functions ware simulated and their impact on system performance is evaluated in both local and wide area scenarios. The results suggest that in practice multiuser LTE is able to support multi stream transmission with very high data rates, even for small hand held terminals. Moreover, the improvements of 4x2 MIMO transmissions for different system configurations are clearly shown over different MIMO channel environments. In depth analysis of the individual system characteristics indicates that these performance differences are due to rather uniform contributions from a set of distinctive features.

Simulation of a Feasible Galileo System Operating in L1 and E5 Bands

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.

Simulation, modeling, and performance analysis of IEEE 802.16e OFDMA Systems for Urban and Rural Environments

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.

Cross-cultural Adaptation and Validation of the Greek Voice Handicap Index-10 (GVHI-10) With Additional Receiver Operating Characteristic Analysis

OBJECTIVE(S) The use of subjective evaluation tools are proven useful and of high clinical value in the case of voice disordered population. For that type of evaluation, self-assessment questionnaires about the severity of the voice like Voice Handicap Index-30 (VHI-30) have been developed. The VHI-30 is the most studied tool which includes psychometrically robustness while guiding physicians therapeutic decision making. Additionally, a valid abbreviated version of VHI-30 was developed for the first time in the Greek Language which is named as Greek Voice Handicap Index-10 (GVHI-10). Consequently, the aim of our study was to validate the proposed version of the VHI-10. METHODS Ninety nondysphonic individuals and 90 dysphonic patients were classified by Otolaryngologists and Speech Language Pathologists. The studys subjects were evaluated with endoscopy and stroboscopy. Also, they were administrated the GVHI-30 and the translated version of the Voice Evaluation Template (VEF). The GVHI-10 was extracted by the Greek version of VHI-30. RESULTS The group with voice disorders exhibited higher statistical significance in all GVHI-10 scores compared to those of the control group. The GVHI-10 showed a high internal consistency (Cronbachs a = 0.915 and split-half reliability coefficient equal to 0.86), good sensitivity compared to Greek VHI-30 (r = 0.764, P = 0.000) and intraclass correlation. A total cut-off point equal to 6.50 (AUC: 0.964; P < 0.001) was also calculated. CONCLUSIONS The proposed version of GVHI-10 distinguished the perceived levels of voice between dysphonic and nondysphonic groups and between different voice disordered populations. The GVHI-10 is shown to be clinically valid and sensitive exhibiting high reliability.

The Design of a Mobile System for Voice e-Assessment and Vocal Hygiene e-Training

Voice assessment is a complicated process and requires high level of expertise. Any attempt of designing and developing a mobile system dealing with voice evaluation and vocal hygiene e-training has to overcome various difficulties. The aim of this study, is to investigate the design of a mobile system with the knowledge on early voice evaluation and vocal hygiene. The user will have feedback on his/her voice profile and hygiene and if necessary will be pointed to consult an appropriate clinician (i.e. ear nose throat physician, gastroenterologist, speech therapist, and psychologist). The methodology tool is based on expert systems. The system’s knowledge acquisition on voice assessment and hygiene is acquired by a combination of the literature, empirical data and interdisciplinary experts’ collaboration. The system includes voice processing and user’s voice self-perception providing findings and suggestions towards a better well-being.

A Broadband CPW-Fed Printed Single-Patch Antenna for Galileo Applications

In this research work a novel and compact broadband U-shaped CPW-Fed single-patch antenna is proposed for Galileo applications. The enhanced performance of the single patch antenna relevant to Galileo signal reception and coverage is presented through simulation and analysis using Microwave Office for the purpose of establishing in depth the benefits of antennas in modern navigation apparatus and applications. The proposed antenna has a center frequency in 1.351 GHz and offers a return loss of better than -10dB from 1.1 to 1.6 GHz. Moreover, satisfactory radiation pattern is obtained through simulation. The proposed patch antenna is suitable for implementing low cost, high stable and well circular polarized Galileo antenna, as demonstrated by numerical simulations.