In May 2004, Dr. Sajid joined the Graz University of Technology, Austria as a doctoral researcher and started his research career within the domain of "Optical Wireless Communications". He completed his doctoral thesis in June 2007 and was awarded the PhD in Electrical Engineering with Excellence. His PhD thesis was well appreciated by fellow scientists in the optical wireless community and it is on their insistence that the doctoral thesis is now being published as a book in 2010. The research within this thesis revolves around the modem design techniques for Terrestrial Free Space Optical (FSO) systems and the channel modeling of these systems. The thesis investigates the challenging problems of fog attenuation analysis, coded modulation techniques and channel capacity evaluation. The thesis has led to further scientific work particularly in the domain of channel modelling and higher state PPM modulation techniques for utilization in Terrestrial FSO systems.