Spiros N. Livieratos

Channel Model for Satellite Communication Links Above 10GHz Based on Weibull Distribution

Modern satellite communication networks will employ frequencies above 10GHz. At these frequency bands, rain attenuation is the dominant fading mechanism. In this paper, a novel channel model, a synthesizer for generating rain attenuation time series for satellite links operating at 10GHz and above is presented. The proposed channel model modifies Maseng-Bakken (M-B) model since it generates rain attenuation time series that follow the Weibull distribution. The new stochastic dynamic model is based on the first-order Stochastic Differential Equations (SDEs) and considers rain attenuation induced on a slant path as a Weibull-based stochastic process. Moreover, the theoretical expressions for the computation of the exceedance probability of hitting time random variable are presented. The hitting time statistics may be employed for the optimum design of Fade Mitigation Techniques (FMTs). The synthesizer is verified in terms of the exceedance probability and the theoretical CCDF of hitting time comparing to these derived from the simulations in the numerical results section.

On the Outage Probability Prediction of Time Diversity Scheme in Broadband Satellite Communication Systems

A novel model for the outage probability prediction in time diversity satellite communication (SatCom) systems operating above 10GHz is proposed. Due to the migration of operating frequency at Ka band and above, atmospheric phenomena afiect the signal. Rain is the dominant fading mechanism. Diversity techniques are the probable solution of the compensation of rain fading. Among the diversity techniques, time diversity has been identifled as an e-cient and cost efiective technique. A method for the prediction of outage performance and diversity gain of time diversity SatCom systems is presented based on the physical assumptions of a well accepted dynamic stochastic model. The new method is tested against with simulated and experimental data with encouraging results.

Time diversity prediction modeling using Copula functions for satellite communication systems operating above 10GHz

In this paper, a new model based on Copula functions for modeling joint exceedance probability of rain attenuation for time diversity satellite systems is presented. Time diversity is an efficient fade mitigation technique, which exploits the decrease of correlation of rainfall medium within time. Copulas theory is used for the coupling of rain attenuation random variables which are considered correlated. The performance of five Copulas on experimental time diversity data is investigated in this paper. The results are very encouraging. Moreover, a significant result is that different copulas must be used depending on the values of the considered time lags. Finally, some useful conclusions are drawn.

Powerful pedagogical approaches for finding Thevenin and Norton equivalent circuits for linear electric circuits

This paper presents two powerful pedagogical approaches for finding Thevenin and Norton equivalent circuits for d.c. linear electric circuits. These approaches are based solely on mesh analysis (for planar circuits) and on nodal analysis (for planar or nonplanar circuits) and simultaneously provide all equivalent circuit parameters from one circuit.

Rain attenuation hitting time statistical distribution: Application to Fade Mitigation Techniques of Future Satellite Communication Systems

Rain attenuation is the dominant fading mechanism for Future Broadband Satellite Communication Systems (operating at Ku band and above). In this paper, hitting time statistics of rain attenuation process are presented using a well accepted dynamic model. Hitting time gives the time needed for a stochastic process to exit an interval of thresholds given the initial value. The expression to compute analytically the Complementary Cumulative Distribution Function (CCDF) of hitting times for rain attenuation is given. Moreover, the employment of hitting time statistics in designing Fade Mitigation Techniques (FMTs) is proposed and a discussion of how these statistics can be used for the FMT control loop is made. The FMTs under consideration for the application of hitting time statistics are the power control, adaptive coding and modulation (ACM) and time diversity. Furthermore, numerical results are presented showing that the theoretical model actually reproduces the hitting time statistics and finally some useful conclusions are drawn.

Dynamic Properties of Rain Attenuation in Athens, Greece: Slant Path Rain Attenuation Synthesizer and Dynamic Diversity Gain

In this paper, the dynamics of rain attenuation are examined, and dynamic diversity gain is evaluated for a pico-scale site diversity system. Since modern satellite communication systems operate at frequencies above 10 GHz, their efficient design requires the adoption of Propagation Impairment Mitigation techniques and so rain attenuation time series synthesizers. For rain attenuation, which is the most dominant fading mechanism, the dynamic stochastic model, proposed by Maseng-Bakken, based on the lognormal distribution is the most widely accepted and used. In this latter model, the dynamic parameter is required for the generation of slant path rain attenuation time series. In this paper, firstly, a simple expression is proposed for the calculation of the dynamic parameter in terms of the mean wind speed, elevation angle of the link, and dynamic parameter of rainfall rate. The new theoretical expression is tested with simulated data with very encouraging results. This expression is then used into a unified rain attenuation synthesizer with inputs from the rainfall rate statistics and the satellite slant path characteristics. Finally, the dynamic diversity gain is calculated for pico-scale site diversity systems for various link characteristics.

Spatially Correlated Multi-modal Wireless Sensor Networks: A Coalitional Game Theoretic Approach

A coalition formation game theoretic method is proposed for efficient multi-service clustering and power control in QoS constrained Wireless Sensor Networks. The method is initiated by the wireless sensor nodes in a distributed way and, next, is successively optimized by a set of powerful nodes called representatives. The proposed method manages the inherent trade-off between energy efficiency and data accuracy to increase WSN lifetime at the cost of controllable loss of accuracy. Simulation results show that the proposed coalition formation method significantly increases WSN lifetime without necessitating significant communications overhead.

Correlated Phenomena in Wireless Communications: A Copula Approach

Copulas are multivariate joint distributions of random variables with uniform marginal distributions. A quite interesting topic in statistical modelling is how the inefficiencies, appearing when the classical linear (Pearson) correlation coefficient is employed, can be overcome. Copulas are increasingly being involved to address such challenges. In the present article, the concept of copulas is employed in the framework of wireless communications and is related to multivariate correlated fading phenomena as well as to the relevant fade mitigation techniques. The multivariate copula-based models employed in the present work are general and can be customized to any continuous multivariate random variables.