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

Abstract

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. Keywords: energy-efficiency, Radio-over-Fiber, in-building networks. INTRODUCTIONThe need to reduce the carbon footprint of telecommunication networks is widely recognized [1,2]. Recent studies reveal that the power consumption of data centers is comparable to that of in-building networks (residential and office) due to the large number of buildings and the spreading Internet literacy of their users [1]. By year 2017, 55% of all IP traffic will originate from wireless and mobile devices [3]. Furthermore, two-thirds of all IP traffic will be consumer traffic originating from households, universities and Internet cafes. This means that the main source of extensive wireless Internet traffic will be from in-building IT networks. Thus, it is important to explore ways for reducing the energy consumption of office and residential building networks. Due to the large number of in-building networks, even a small decrease in the energy consumption in each of the individual networks would lead to a significant decrease in the overall energy consumption.Wireless communications enables mobile access to the Internet; however, it has limited bandwidth and suffers from inherent energy loss due to its broadcast nature rendering it fundamentally energy inefficient compared to wired transmission links such as optical links. In contrast, optical links offer very high-speed access to the Internet with low energy loss, but cannot offer user mobility. Consequently, optical/wireless convergence is seen as an ideal candidate for increasing the network bandwidth, decreasing its energy consumption and offering end-user mobility. Radio-over-Fiber (RoF) is a promising technology for the implementation of seamless and energy-efficient optical/wireless networks [2].In this paper, we study the physical limits of both optical and wireless transmission links and their impact on the power consumption of the network as a whole. We show that there is an optimum cell size for an op...