Centralized Optical Routing based on Digitized Radio-over-Fiber Technique for Wireless Backhauling

The abrupt adaptation of smart devices combined with the demands for seamless connections and high quality multimedia services gave rise to today's explosion of wireless data traffic. Most of the wireless traffic is generated at in-building environment such as airport, shopping center, or office district. To handle this increasing in-building wireless traffic properly, low-cost, high-efficient, and low-energy consuming wireless backhauling infrastructures are essential. In next generation in-building wireless backhauling infrastructures, therefore, a cellular coverage and radiation power should be much smaller over limited spectral bandwidth such as pico- and femto-cell. Recently the digitized Radio-over-Fiber (D-RoF) technique has been introduced as a candidate for a next generation wireless backhaul. In D-RoF system, analog wireless signals are transmitted over optical fiber links in the form of digital baseband that is free from the drawbacks of analog counterpart [1]. As a wireless backhaul, a D-RoF system can extend wireless pico-cells to each room instead of a single wireless network. In addition, different multimedia services to the individual destinations (rooms) and multiple sub-networks with a small number of rooms can be established by combining with the centralized optical interconnection. By adjusting optical connectivity and RF frequency allocation, wireless cells in a building can be dynamically changed in size and capacity. Such dynamic provisioning of capacity to each cell can significantly improve the operational efficiency of the wireless backhaul network[2]. In this paper, we present the demonstration of an in-building wireless backhaul based on the D-RoF technique with the centralized optical routing for dynamic capacity allocation to each wireless cell. As a proof of concept, we have shown the selective optical routing of WiMAX compatible signal (16-QAM, 6MSps @2.475GHz) over the digitized RoF link. To verify the performance of the proposed system, the error-vector magnitude (EVM) of the recovered WiMAX signal at the digitized- and analog- RoF system under nonlinear operations such as the wavelength conversion of semi-conductor amplifier (SOA)s has been compared; the digitized RoF system shows robust performances with constant EVM (~3.75%) regardless of optical channel conditions while the performance of the analog RoF varies as optical channel conditions.