Green optical/wireless in-building networks: The physics of design

Energy efficiency is rapidly becoming an important requirement for modern networks. In this paper, we discuss the physical limits to the power consumption of wireless and optical transmission. We show that there is an optimum cell size that results in the least power consumption in optical/wireless in-building networks and explain why. We then discuss the principles that govern the design of in-building Radio-over-Fiber (RoF) distribution networks. We use theoretical models to analyze the impact of key design factors on the energy consumption of point-to-point RoF links and how their adverse effects can be mitigated. Finally, we compare the energy consumption of several key in-building optical/wireless architectures based on several different RoF technologies, and demonstrate that centralized architectures based on RoF links can be substantially more energy efficient than baseband-over-fiber (BoF) architectures in network capacity-limited scenarios, when designed properly. Our findings also show that RoF-based architectures are energy efficient for cell sizes less than 10m.