University of Piraeus

About: University of Piraeus is a education organization based out in Piraeus, Attiki, Greece. It is known for research contribution in the topics: Context (language use) & Computer science. The organization has 1731 authors who have published 6209 publications receiving 106699 citations.

Reconfigurable Orthonormal Basis Patterns Using ESPAR Antennas

Abstract: Beamspace multiple-input-multiple-output (BS-MIMO) systems with reduced hardware complexity have been recently considered in the literature. So far, BS-MIMO research effort focuses on the development of efficient single-RF MIMO transmission schemes based on parasitic antenna arrays. Single-RF BS-MIMO systems can provide both multiplexing and beamforming capabilities by exploiting the available aerial degrees of freedom of the radiated field while maintaining low space and complexity requirements. Previous studies used electronically steerable passive array radiators (ESPARs) for the multiplexing of multiple data streams utilizing an ESPAR-specific set of orthonormal basis patterns. However, these basis patterns ensure orthogonal transmission of the multiple streams in idealistic rich scattering environments. In this letter, a novel technique is developed for the adaptive selection of the most effective basis patterns in both transmitter and receiver sides based on the actual wireless channel propagation conditions maximizing the system capacity.

Forecasting short-term freight rate cycles: do we have a more appropriate method than a normal distribution?

Abstract: General economists, as well as Maritime economists, assume that the time series they forecast follow normal distribution, and data is independently and identically distributed around the mean. This paper contests this assumption with the aid of three sets of time series: (1) The Dry Cargo Freight Index, 1741–2005: in this series the data deviate from the mean by more than three standard deviations on no fewer than six occasions, and exhibited “fat tails”; (2) The time charter freight rates for a 10-year-old, 80 000 dwt vessel from 6 January 1989 to 26 December 2008: this series also exhibits skewness and kurtosis in a leptokurtic distribution; and (3) The Dry Cargo Time Charter Index from 1971 to 2004: this series diverged from the normal distribution four times. Next, we searched more recent data for short-term cycles using the V-statistic. One cycle was found to last 4 years (2005 to 2008), which is in accordance with theory. This cycle started on 29 July 2005 and ended when it reached the (lowest) leve...