Optical Signal Processing Techniques for Radio over Fiber System to Increase Coverage and Capacity

At present the information age is ruled by the Internet, where all types of businesses, entertainment industry and political change is hugely shaped and influenced by the social media and the search engines. For instance, the worldwide introduction of smart-phones, Tablet PCs and the cloud paradigms for computing and data storage has directed more and more subscribers to require Internet connection (Wi-Fi, 4G) wirelessly. Large coverage and capacity, online connectivity and high mobility requirements can be fullfilled by exploiting the benefits of both millimeter-wave (mm-wave) frequencies and optical fibers. Optical fiber communication systems offer long-haul and high bandwidth transmission and the use of mm-wave frequencies provides huge bandwidth in the wireless domain. To achieve the distribution of mm-wave signals in distributed antenna system (DAS) architecture a considerable attention has been dedicated to the transmission of radio frequency (RF) signals through optical fiber systems. The amalgam of RF and optical fiber technologies has given the birth of radio over fiber (RoF) systems.

Since high-frequency signals travel shorter distances due to their higher path-loss, the cell sizes have to be further reduced. This reduction in cell size implies that more Radio Access Units (RAUs) are required for the increased number of cells, which are located close to each other. Additionally, signal processing is required at each RAU which increases the cost and complexity of the system. Hence, it is appropriate to have simple RAUs which are linked with a central unit (CU) in a centralized DAS architecture. All the resource management and signal processing can be jointly done at CU, where RAUs act as the basic elements of the coordinated multi-point (CoMP) architecture. In this situation, the connectivity between the CU and RAUs is done by the ROF technologies. ROF links are suitable for the transmission of high frequency radio signals over fiber because of their transparency to the type of RF signal, low attenuation and enormous bandwidth. In this thesis ROF based communication system has been investigated.