C-RAN and virtualized Small Cell technology poses several major research challenges. These include dynamic resource allocation, self-configuration in the baseband pool, high latency in data transfer between radio unit and baseband unit, the cost of data delivery, high volume of data in the network, software networking aspects, potential energy savings, security concerns, privacy of user's personal data at a remote place, limitations of virtualized environment, etc. This book provides deeper insights into the next generation RAN architecture and surveys the coexistence of SDN, C-RAN and Small Cells solutions proposed in the literature at different levels.