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

Capacity of and coding for multiple-aperture, wireless, optical communications

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (p. 243-249).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Refractive index turbulence causes random power fluctuations in optical communication systems, making communication through the atmosphere difficult. This same phenomenon makes the stars twinkle at night, and pavement shimmer on a hot summer day. True to the old adage, "don't put all your eggs in one basket," we examine laser communication systems that use multiple transmit and receive apertures. These apertures provide redundant replicas of the transmitted message to the receiver, each corrupted separately by the atmosphere. Reliable communication occurs when not all of these paths are deeply faded. We quantify the maximum rate of reliable communication, or capacity, and study space-time coding techniques for both direct- and coherent-detection receivers. We also experimentally verify the performance of some simple techniques for optically-preamplified, direct-detection receivers.by Shane M. Haas.Ph.D

Subcarrier intensity modulated free-space optical communication systems

This thesis investigates and analyses the performance of terrestrial free-space optical communication (FSO) system based on the phase shift keying pre-modulated subcarrier intensity modulation (SIM). The results are theoretically and experimentally compared with the classical On-Off keying (OOK) modulated FSO system in the presence of atmospheric turbulence. The performance analysis is based on the bit error rate (BER) and outage probability metrics. Optical signal traversing the atmospheric channel suffers attenuation due to scattering and absorption of the signal by aerosols, fog, atmospheric gases and precipitation. In the event of thick fog, the atmospheric attenuation coefficient exceeds 100 dB/km, this potentially limits the achievable FSO link length to less than 1 kilometre. But even in clear atmospheric conditions when signal absorption and scattering are less severe with a combined attenuation coefficient of less than 1 dB/km, the atmospheric turbulence significantly impairs the achievable error rate, the outage probability and the available link margin of a terrestrial FSO communication system. The effect of atmospheric turbulence on the symbol detection of an OOK based terrestrial FSO system is presented analytically and experimentally verified. It was found that atmospheric turbulence induced channel fading will require the OOK threshold detector to have the knowledge of the channel fading strength and noise levels if the detection error is to be reduced to its barest minimum. This poses a serious design difficulty that can be circumvented by employing phase shift keying (PSK) pre-modulated SIM. The results of the analysis and experiments showed that for a binary PSK-SIM based FSO system, the symbol detection threshold level does not require the knowledge of the channel fading strength or noise level. As such, the threshold level is fixed at the zero mark in the presence or absence of atmospheric turbulence. Also for the full and seamless integration of FSO into the access network, a study of SIM-FSO performance becomes compelling because existing networks already contain subcarrier-like signals such as radio over fibre and cable television signals. The use of multiple subcarrier signals as a means of increasing the throughput/capacity is also investigated and the effect of optical source nonlinearity is found to result in intermodulation distortion. The intermodulation distortion can impose a BER floor of up to 10-4 on the system error performance. In addition, spatial diversity and subcarrier delay diversity techniques are studied as means of ameliorating the effect of atmospheric turbulence on the error and outage performance of SIM-FSO systems. The three spatial diversity linear combining techniques analysed are maximum ratio combining, equal gain combining and selection combining. The system performance based on each of these combining techniques is presented and compared under different strengths of atmospheric turbulence. The results predicted that achieving a 4 km SIM-FSO link length with no diversity technique will require about 12 dB of power more than using a 4 × 4 transmitter/receiver array system with the same data rate in a weak turbulent atmospheric channel. On the other hand, retransmitting the delayed copy of the data once on a different subcarrier frequency was found to result in a gain of up to 4.5 dB in weak atmospheric turbulence channel

Advanced Trends in Wireless Communications

Physical limitations on wireless communication channels impose huge challenges to reliable communication. Bandwidth limitations, propagation loss, noise and interference make the wireless channel a narrow pipe that does not readily accommodate rapid flow of data. Thus, researches aim to design systems that are suitable to operate in such channels, in order to have high performance quality of service. Also, the mobility of the communication systems requires further investigations to reduce the complexity and the power consumption of the receiver. This book aims to provide highlights of the current research in the field of wireless communications. The subjects discussed are very valuable to communication researchers rather than researchers in the wireless related areas. The book chapters cover a wide range of wireless communication topics

Error performance analysis of cross QAM and space-time labeling diversity for cross QAM.

Doctoral Degrees. University of KwaZulu-Natal, Durban.Abstract available in the PD