Copyright and Reference Information: This material (preprint, accepted manuscript, or other author-distributable version) is provided to ensure timely dissemination of scholarly work. Copyright and all rights therein are retained by the author(s) and/or other copyright holders. All persons copying this work are expected to adhere to the terms and constraints invoked by these copyrights. This work is for personal use only and may not be redistributed without the explicit permission of the copyright holder. The definite version of this work is published as [·] Yahya Al-Hazmi, Hermann De Meer, Karin A. Hummel, Harald Meyer, Michela Meo and David Remondo. Energy-efficient wireless mesh infrastructures. IEEE Network Magazine, Volume [NA], pages [NA], April 2011. to appear. See http://www.net.fim.uni- passau.de/papers/Al- Hazmi2011a for full reference details (BibTeX, XML). Energy-Efficient Wireless Mesh Infrastructures Yahya Al-Hazmi and Hermann de Meer University of Passau Innstr. 43, 94032 Passau, Germany {yahya.al-hazmi, hermann.demeer}@uni-passau.de Michela Meo Politecnico di Torino C.so Duca degli Abruzzi 24, Torino, Italy michela.meo@polito.it Karin Anna Hummel and Harald Meyer University of Vienna Lenaugasse 2/8, 1080 Vienna, Austria {karin.hummel, harald.meyer}@univie.ac.at David Remondo UPC - Barcelona Tech 08860 Castelldefels, Spain remondo@entel.upc.es Abstract—The Internet comprises access segments with wired and wireless technologies. In the future, we can expect Wireless Mesh Infrastructures (WMIs) to proliferate in this context. Due to the relatively low energy efficiency of wireless transmission, as compared to wired transmission, energy consumption of WMIs can represent a significant part of the energy consumption of the Internet as a whole. We explore different approaches to reduce energy consumption in WMIs, taking into account the heterogeneity of the technologies and the interaction with wired networks. Finally, we present an example scenario where the application of these methods is discussed. I. I NTRODUCTION AND CONCEPTS Internet traffic is steadily growing due to the increasing number of users and the higher service demands. At the same time, energy consumption has become a key social and political issue. Therefore, the energy consumption of the Internet might represent a fundamental constraint for its future growth. The Internet comprises three segments: the core, metropoli- tan/edge, and access segments. The core network comprises large routers, linked with high-capacity Wavelength-Division Multiplexing (WDM) optical fibres. The metropolitan segment constitutes the bridge between the access network and the core network; it is connected to the core network via several edge routers and it contains several edge nodes connected to the access network. Currently, this segment comprises electronic switches, but there is very active research on optical network- ing solutions such as Optical Burst Switching (OBS) or Optical Packet Switching (OPS). The access network connects user terminals with the edge node. Multiple technologies are em- ployed nowadays and this can be expected to be the scenario in years to come. The Digital Subscriber Line (DSL) technology is gradually being replaced by optical fibre. Although in some cases DSL is replaced partially, forming what is called Fibre-to-the-Node (FTTN), the general evolution is towards Point-to-Point (PtP) optical fibre or the more economical and robust Passive Optical Network (PON) technology, as shown in Fig. 1. In PON, an Optical Line Terminal (OLT) is located at the local exchange and is connected to several Optical Network Units (ONUs). Each ONU is linked to the OLT through a different fibre, but the fibres are joined together by a passive splitter into a common fibre to the OLT. Recent developments in wireless technologies have made them attractive as part of the access segment of the Internet. The main attractiveness of wireless technology for the access results from its flexibility, permitting in most cases terminal mobility and saving on infrastructure for the operator. On the one hand, cellular systems have evolved towards more efficient data transmission, and today can be useful for some data services. On the other hand, IEEE 802.11 (WiFi) technol- ogy has become widespread and its maximum link capacity matches that of some wired technologies. Additionally, new technologies have become available, such as IEEE 802.16 (WiMAX), with Base Station (BS) capacities close to those of ONUs. The wired and the wireless technologies in the access segment can be combined in order to increase resource uti- lization efficiency while satisfying the user’s demands. We expect future access networks where ONUs are integrated with WiMAX BSs, WiFi Access Points (APs), or new-generation cellular BSs. These wireless nodes could be connected to form a Wireless Mesh Infrastructure (WMI), as shown in Fig. 1. The WMI is formed by a set of static, wireless devices, which we call Wireless Mesh Nodes (WMNs). User terminals, which can be either static, nomadic or mobile, connect to a WMN via one wireless hop, thereby alleviating the complexity of multihop wireless routes involving several mobile devices and relieving the user terminals from forwarding third-party packets. WMNs route and forward packets between different user terminals or between these and the wired access segment, with the ability of using several wireless hops if needed. WMNs may have multiple interfaces. We can expect WMIs to become widespread in future access networks, since they are easier and more economical to deploy than fibre, they provide a more pervasive connectivity as compared to wired access, they have higher flexibility than homogeneous access infrastructures, and they enjoy lower complexity and increased resource efficiency as compared to Mobile Ad hoc NETworks (MANETs). Despite the mentioned advantages of WMIs, in the next section we will see that the energy efficiency of wireless