Contrasting space-time schemes for MIMO FSO systems with non-coherent modulation

International audienc

GEOPHYSICAL INVESTIGATION FOR GROUND WATER DEVELOPMENT WITHIN THE PREMISES OF ABUAD INTERNATIONAL SCHOOL, AFE BABALOLA UNIVERSITY, ADO-EKITI, EKITI STATE, NIGERIA

A geophysical investigation is necessary for groundwater development in Basement complex areas like ABUAD International School of Afe Babalola University due to varied geological properties of the underlying aquifers present. A Vertical Electrical Sounding (VES) electrical resistivity method was adopted within the study area. Vertical Eletrical sounding using Schlumberger array was conducted at (6) VES stations. The study was carried out to determine the sub surface layer resistivity and thickness in order to use same to categorize the groundwater potential of the study area. The field data obtained were analysed using the winResist computer software which gives an automatic interpretation and plotting of the apparent resistivity. Generally, results obtained revealed four subsurface/geoelectric layers which are topsoil, hardpan/lateritic clay, weathered basement and fractured basement. The depth to the basement (overburden thickness) beneath the sounding stations is assumed to include the topsoil, lateritic clay and weathered/fractured rock. The values range from 1.0m to 17.9m with an average thickness value of 12.0m. It can be concluded that the low resistivity and significantly thick weathered rock/clay and the fractured basement constitute the aquifer in this area. Results from this study have revealed that The location around the VES 3, 5, & 6 points are the most promising region for borehole development and the estimated depth of the borehole is 60-65m deep and the overburden btw 9.9 – 12.9

Ground‐to‐GEO optical feeder links for very high throughput satellite networks: Accent on diversity techniques

This paper studies the use of optical feeder links in very high throughput satellites (VHTS) networks with emphasis on gateway diversity techniques to mitigate the inherent propagation losses in optical frequencies. Focusing on a GEO scenario, the paper considers a system‐wide approach investigating various challenges of optical feeder links. These include transmission schemes amenable for transparent on‐board processing, optical channel models taking into account blockage by clouds and fading caused by atmospheric turbulence in addition to complexity of on‐board and on‐ground processing. The channel models are then used to dimension the ground segment towards ensuring a given availability percentage (e.g., 99.9%). The channel model and payload complexity further influence the choice of link layer techniques used for counteracting fading due to atmospheric turbulence in the absence of blockage. An elaborate end‐to‐end simulator incorporating the proposed channel models capturing the nuances of various processing blocks like optical‐electrical conversion is developed. The system performance results provide interesting insights and a framework for assessing the feasibility and advantages of optical feeder links in VHTS systems

Optical wireless MIMO communication

This thesis provides an in-depth investigation and evaluation of infrared optical wireless MIMO communication systems to be applied in both indoor and outdoor environment. The principle objective of the research is to demonstrate both the advantages and disadvantages of the optical wireless MIMO systems using different modulation types. The first part provided analyses of important OW configurations using APD receivers using WMC model and SISO, MISO, SIMO and MIMO configuration. Thus, an analytical expression for 2-1 MISO, 1-2 SIMO and MIMO was successfully developed. This part also illustrates the coding gains possible using diversity schemes for APD OW systems. In the presence of strong fading, the SISO approach is rendered virtually useless, whereas diversity offers acceptable BER values. The results underpin the approach of this thesis, where indoor PIN diode based experimental measurements confirm the gains offered by diversity. In the second part of the work, several optical wireless MIMO systems applicable for the indoor environment are developed for three different modulation types, OOK modulation, PPM modulation and SIR-RZI modulation. These modulations are used in optical MIMO systems are studied for which, mathematical models that evaluate the BER performance of the MIMO system for different axis displacement and for different distances between transmitters and receivers. Based on the results, the PPM system has been shown to present the best BER performance, including high interference-resistance capability. A group of new mathematical models have been evaluated, which demonstrates a high level of correlation with the results derived from empirical models at 93%. Thus, the mathematical models developed and used for the specified evaluation appear to correspond reasonably well, and can be applied in future research on these aspects