Dietrich Zeller

Challenges and enabling technologies for energy aware mobile radio networks

Mobile communications are increasingly contributing to global energy consumption. In this article, a holistic approach for energy efficient mobile radio networks is presented. The matter of having appropriate metrics and evaluation methods that allow assessing the energy efficiency of the entire system is discussed. The mutual supplementary saving concepts comprise component, link and network levels. At the component level the power amplifier complemented by a transceiver and a digital platform supporting advanced power management are key to efficient radio implementations. Discontinuous transmission by base stations, where hardware components are switched off, facilitate energy efficient operation at the link level. At the network level, the potential for reducing energy consumption is in the layout of networks and their management, that take into account slowly changing daily load patterns, as well as highly dynamic traffic fluctuations. Moreover, research has to analyze new disruptive architectural approaches, including multi-hop transmission, ad-hoc meshed networks, terminal-to-terminal communications, and cooperative multipoint architectures.

EARTH — Energy Aware Radio and Network Technologies

EARTH is a major new European research project starting in 2010 with 15 partners from 10 countries. Its main technical objective is to achieve a reduction of the overall energy consumption of mobile broadband networks by 50%. In contrast to previous efforts, EARTH regards both network aspects and individual radio components from a holistic point of view. Considering that the signal strength strongly decreases with the distance to the base station, small cells are more energy efficient than large cells. EARTH will develop corresponding deployment strategies as well as management algorithms and protocols on the network level. On the component level, the project focuses on base station optimizations as power amplifiers consume the most energy in the system. A power efficient transceiver will be developed that adapts to changing traffic load for an energy efficient operation in mobile radio systems. With these results EARTH will reduce energy costs and carbon dioxide emissions and will thus enable a sustainable increase of mobile data rates.

Approaches to energy efficient wireless access networks

Due to increasing data traffic rates and rollout of advanced radio transmission technologies wireless networks consume increasing amount of energy and contribute a growing fraction to the CO2 emissions of ICT industry. Thus, climate and cost issues now shift the research focus of wireless communications to energy consumption and energy efficiency. Two approaches can be followed: Incremental improvements of existing systems or a clean slate re-design with a fundamental change of paradigms. We describe two such initiatives and discuss their differences. The EC FP7 project EARTH is a 30 month project aiming for a reduction of the overall energy consumption of 4G mobile broadband networks by 50%, regarding network aspects and individual radio components from a holistic point of view. The Green Touch Initiative is a privately financed consortium addressing fundamental research that will pave the way to much higher reductions for future systems in the order of several magnitudes, with first proof of concepts available in 5 years.

Enablers for Energy Efficient Wireless Networks

Mobile communications are increasingly contributing to global energy consumption. The EARTH (Energy Aware Radio and neTworking tecHnologies) project tackles the important issue of reducing CO2 emissions by enhancing the energy efficiency of cellular mobile networks. EARTH is a holistic approach to develop a new generation of energy efficient products, components, deployment strategies and energy-aware network management solutions. In this paper the holistic EARTH approach to energy efficient mobile communication systems is introduced. Performance metrics are studied so to assess the theoretical bounds of energy efficiency and the practical achievable limits. Moreover, various deployment strategies focusing on their potential to reduce energy consumption are studied, whilst providing uncompromised coverage and user experience. This includes heterogeneous networks with a sophisticated mix of different cell sizes, which may be further enhanced by energy efficient relaying and base station cooperation technologies. Finally, scenarios leveraging the capability of advanced terminals to operate on multiple radio access technologies (RAT) are discussed with respect to their energy savings potential.

Multimedia broadcast multicast service: new transmission schemes and related challenges

MBMS (Multimedia Broadcast Multicast Service) is a service offered by 3GPP (3rd Generation Partnership Project) cellular networks for the distribution of multimedia content and competes with technologies like DVB-H (Digital Video Broadcasting - Handhelds) and DMB (Digital Multimedia Broadcasting). For MBMS in LTE (Long Term Evolution), 3GPP discussed two different radio transmission schemes: one with cells transmitting in an uncoordinated way and one with cells synchronously transmitting such that signals from several cells are perceived as one signal at the user terminal. We will discuss related challenges such as the choice of a suitable transmission scheme, the coordination of base stations for the synchronized transmission of content, and mobility between areas of different transmission schemes.

Uniform MAC headers for synchronized MBMS transmission

MBMS (Multimedia Broadcast Multicast Service) is a service offered by 3GPP cellular networks for the distribution of multimedia content and can be transmitted by multiple base stations in a coordinated way such that signals from several base stations are perceived as one single signal at the user terminal. This requires synchronization of the radio interface on all layers so that all participating base stations have to apply the same transmission rules to the packets they obtain from the core network. These rules must be robust in the sense that synchronization is maintained even if some packets are not received by a base station. In this paper we propose a corresponding method that is capable of reliably accommodating the loss of an arbitrary number of consecutive packets even if statistical multiplexing is applied.

Fat pipes for user plane tunneling in 5G

The main service of current mobile networks is to transport user data packets between the user devices and external packet data networks. This is done by using transport tunnels which in todays networks are based on the GPRS Tunneling Protocol User Plane (GTP-U) or the Generic Routing Encapsulation (GRE) protocol. These user plane tunnels are denoted as “thin pipes” as they carry only the data of a single user data flow. The tunnels must be setup each time when a UE enters the active mode or starts a session with new service requirements. This is very inefficient especially when a UE transmits small amounts of data only sporadically which is the case e.g. for Machine Type Communication. In contrast to these thin pipes, “fat pipes” using Ethernet over GRE (EoGRE) tunneling can carry the data flows of different users with similar service requirements in the same tunnel. The advantage is that with fat pipes, the amount of control signaling is strongly reduced because the setup and maintenance of user specific tunnels (thin pipes) is avoided. As a second advantage, the Ethernet layer natively supports the transport of IP-as well as of non-IP data. Therefore, this paper proposes to use EoGRE based fat pipes on all network internal interfaces carrying user plane traffic. To enable this solution, this paper further proposes a mapping mechanism of 3GPP based identifiers like temporary mobile subscriber identities to IEEE 802 MAC addresses so that existing Ethernet based mechanisms for the bridging and routing of user plane data can be used. This mapping mechanism also includes a so-called “Network Interface ID” in order to support Multi-Connectivity.

Topologies of wireless mesh networks with inband backhauling

Wireless mesh networks (WMNs) with inband backhauling use the same antennas for the backhaul as well as for the access. Therefore antennas of next hop neighbours need to be directed to each other. However, such a configuration is not possible in a three-sectorized hexagonal cell deployment. In this paper we derive several alternative topologies that are suitable for WMNs with inband backhauling. We show that a topology with four directional antennas per node and backhaul connectivity between indirect neighbours outperforms competing topologies in terms of handover rate, optimal maximum power, and system capacity.