The combination of radio over fiber (RoF) and orthogonal frequency division multiplexing (OFDM) techniques has resulted in a high-data-rate at lower cost in the last mile of wireless networks. This paper investigates the use of the OFDM as a modulation technique for radio over fiber (RoF) in passive optical network (PON). A laser source of 1550 nm wavelength was used with 100 km, 140 km and 288 km single mode fiber. In the OFDM-PON a passive optical splitter of ratio 1:2 is used to connect two optical network units (ONUs). A 10 Gbits/sec transmission bit rate is used to simulate the RoF-OFDM-PON system. The proposed system can provide a flexible, cost effective and significant high data rate.

An increase in the demand of broadband service has encouraged research and study to find a solution to offer an adequate amount of service. Living in this digital world with downloading video, voice or data leads us occasionally to have a shortage of bandwidth in the provided data. One of the solutions to cover the huge expected demand in the future is improving the communication systems by adding optical passive components to the Radio over Fiber (RoF) system. This work is mainly to increase the bandwidth that allows the small and single consumer at the last mile. We have shown that by adding the 40-GHz mm-wave to the system, Bit-Error-Rate (BER) has increased while Q-factor has decreased.

Growing energy demand and environmental concerns have led to an increased interest in renewable energy resources to provide a sustainable and low carbon emission energy supply. Among these renewable energy resources, photovoltaic (PV) systems have been the focus of many scientific researchers. The most vital component of a PV system that needs to be improved is the power converter. Grid-tied transformer-less inverters have gained a lot of interest in recent years because of their higher efficiency, reduced volume and lower cost compared to traditional line transformer inverters. This dissertation discusses single-phase transformer-less inverter challenges and provides solutions that could lead to a next generation, high performance, grid-connected, single-phase transformer-less inverter. A new topology with new current paths is proposed to increase efficiency and reduce the leakage current. A comparison study of the proposed topology and multiple transformer-less inverters is carried out in terms of leakage current, power losses and efficiency. This dissertation also investigates the impact of emerging Gallium Nitride (GaN)based power devices on a single-phase transformer-less inverter in terms of efficiency, high switching frequency capability, volume and cooling efforts. GaN device structure, as well as static and dynamic characterization, are discussed. Furthermore, this dissertation studies GaN power devices' reverse conduction capability to provide the proposed inverter with reactive power control. Existing PWM I would like to start by expressing my deepest gratitude and appreciation to my advisor Dr. Mohammad Matin for his support, advice and encouragement throughout this research. His mentorship and experienced guidance helped me strengthen my research skills. His valuable insight, motivation, and enthusiasm were the most important assets that led to the completion of this research. I also would like to express my sincere appreciation to my dissertation committee members: Dr. Wenzhong Gao, Dr. Amin Khodaei, and Dr. Shimelis Assefa for their invaluable suggestions, comments and advice that helped me throughout my research progress. My deepest thanks, gratitude, and respect go to my parents for a lifetime of unfailing love, encouragement, support and patience. Finally, I would like to thank my loving wife for her endless caring, understanding, and patience during my PhD study. vi

Recently, the interest in grid-tied PV transformer-less inverters has increased rapidly, because of their higher efficiency and lower cost compared to traditional line transformer inverters. This paper presents a new modified transformer-less topology derived from H5 inverter, and provides a detailed comparison between the use of GaN and Si devices for the proposed topology. Detailed operation modes, inverter structure and switching strategy of the proposed topology are presented. Datasheet information, conduction losses, switching losses, and heat sink requirements are studied and analyzed to provide an accurate comparison between GaN and Si power devices for the proposed topology operating at unity power factor. The results show that, GaN power devices significantly reduce the power losses in the system, which consequently allow a significant increase in either inverter power rating or switching frequency. Thus, the use of GaN power devices for the proposed inverter can be more appealing and cost-effective approach.

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