Inter-carrier interference mitigation for underwater acoustic communications

Communicating at a high data rate through the ocean is challenging. Such communications must be acoustic in order to travel long distances. The underwater acoustic channel has a long delay spread, which makes orthogonal frequency division multiplexing (OFDM) an attractive communication scheme. However, the underwater acoustic channel is highly dynamic, which has the potential to introduce significant inter-carrier interference (ICI). This thesis explores a number of means for mitigating ICI in such communication systems. One method that is explored is directly adapted linear turbo ICI cancellation. This scheme uses linear filters in an iterative structure to cancel the interference. Also explored is on-off keyed (OOK) OFDM, which is a signal designed to avoid ICI

A Study of Tears in the Odyssey

In this thesis, I argue that tears function in the Odyssey as an important index of character. I discuss the weepers in three groups: Penelope and the slaves (Chapter 1), Odysseus' companions (Chapter 2), and Odysseus and Telemachos (Chapter 3). Tears characterize the first two groups relative to Odysseus, demonstrating loyalty to/memory of him and serving as foil for his resolve, respectively. Telemachos' few tears link him with his father, who otherwise weeps like no one else in the epic.Master of Art

Wideband spectrum sensing using rapidly tuned antennas

An enabling technology for cognitive radio is expeditious wideband spectrum sensing. A major challenge for implementing wideband spectrum sensors is fitting a wideband antenna within a given form factor. Scanning a narrowband antenna is an attractive alternative to using a wideband antenna in situations where constraints on the allowable antenna dimensions make designing a sensitive wideband antenna a challenge. However, scanning the antenna through a wide spectrum extremely rapidly can induce significant nonlinear effects. This work explores the nonlinear effects of rapidly scanning a narrowband antenna in order to enable the design of devices that scan the antenna extremely rapidly. The frequency spread due to the amplitude modulation effect due to tuning and detuning the antenna is characterized. The frequency shift due to the rapidly changing phase associated with rapidly tuning an antenna is calculated. The limit on how rapidly the antenna may be tuned effectively is explored. The nonlinear effects of rapid antenna tuning are observed experimentally and replicated in simulation

Oxygen and hydrogen ion abundance in the near-Earth magnetosphere: Statistical results on the response to the geomagnetic and solar wind activity conditions

The composition of ions plays a crucial role for the fundamental plasma properties in the terrestrial magnetosphere. We investigate the oxygen-to-hydrogen ratio in the near-Earth magnetosphere from -10 RE<XGSE}< 10 RE. The results are based on seven years of ion flux measurements in the energy range ~10 keV to ~955 keV from the RAPID and CIS instruments on board the Cluster satellites. We find that (1) hydrogen ions at ~10 keV show only a slight correlation with the geomagnetic conditions and interplanetary magnetic field changes. They are best correlated with the solar wind dynamic pressure and density, which is an expected effect of the magnetospheric compression; (2) ~10 keV O+ ion intensities are more strongly affected during disturbed phase of a geomagnetic storm or substorm than >274 keV O+ ion intensities, relative to the corresponding hydrogen intensities; (3) In contrast to ~10 keV ions, the >274 keV O+ ions show the strongest acceleration during growth phase and not during the expansion phase itself. This suggests a connection between the energy input to the magnetosphere and the effective energization of energetic ions during growth phase; (4) The ratio between quiet and disturbed times for the intensities of ion ionospheric outflow is similar to those observed in the near-Earth magnetosphere at >274 keV. Therefore, the increase of the energetic ion intensity during disturbed time is more likely due to the intensification than to the more effective acceleration of the ionospheric source. In conclusion, the energization process in the near-Earth magnetosphere is mass dependent and it is more effective for the heavier ions