Markus Gruber

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.

Vertical Antenna Tilt Optimization for LTE Base Stations

An optimal vertical antenna tilt in a wireless access network plays a key role for coverage and capacity in the system. The autonomous (re-)optimization of tilts bears a large saving potential for operators as manual intervention is particularly costly. In this paper, we present a heuristic variant of the gradient ascent method to continuously optimize antenna tilts with quick convergence. We show that the average spectral efficiency in the system increases by 10% and that the spectral efficiency at the cell edge (5% quantile) increases by 100% after optimization. Changing conditions during the operational phase of the network, as for instance cell outage, can successfully be detected and compensated by an autonomous re-optimization.

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.

Micro base stations in load constrained cellular mobile radio networks

Future cellular mobile radio networks will exhibit a much more dense base station deployment than 2nd or 3rd generation communications systems, particularly with regard to traffic coverage. Hence, a significant increase in power consumption of cellular networks can be expected. In order to counter this trend, energy efficiency of such networks should be increased considerably. Concerning energy efficiency, utilizing micro base stations with their smaller power consumption capabilities appear promising. In this paper we study various homogeneous and heterogeneous deployment strategies incorporating micro base stations with focus on energy efficiency represented by power consumption and throughput. Further, we deal with the impact of different load scenarios on energy efficiency of the various network topologies in more detail.

A survey of autonomic networking architectures: towards a Unified Management Framework

SUMMARY Academic and industrial research initiatives have sought to make fully autonomic networks a reality. Some of these initiatives pursued a holistic approach, while others focused on setting up functionalities for specific networking domains. These efforts did not succeed in being extensively deployed, because the goals of network operators were not satisfactorily met. These goals include unification of management operations, enablement of end-to-end management and enhancement of the overall system performance in a trusted way, while reducing management cost. In this paper, we analyse a set of existing autonomic management architectures and frameworks with respect to a selected set of criteria. We then identify missing parts and challenges and propose a framework to unify the most promising attributes towards a novel approach of realization of autonomic networking management. We call this proposal Unified Management Framework (UMF). Copyright

Autonomous neighbor relation detection and handover optimization in LTE

Handovers require serving cells to have knowledge about the existence of neighboring cells. This information is stored in neighbor relation tables (NRTs), which can be automatically generated during a procedure called automatic neighbor relation (ANR) by leveraging measurements carried out by terminals. We show, using simulations, how fast the NRT converges with respect to the number of terminals and their speeds, as well as how incomplete NRTs influence the handover drop rate. By means of a field trial, we demonstrate that ANR works successfully in a real-life environment. In addition, we investigate solutions for problematic handover scenarios and self-optimization of relevant handover parameters based on decentralized approaches. We show that some handover parameters have more impact on network performance than others. Two promising self-optimization methods are discussed, based on either a cost function or a genetic programming technique which searches for a suitable algorithm that determines the parameters.

Scalability study of ultra-dense networks with access point placement restrictions

Network densification appears to be a scalable means of addressing increasing traffic demands. Indeed, network densification can, at least theoretically, logarithmically increase the delivered traffic in a given area when assuming that access points can be placed arbitrarily close to the users. In practice, however, access points cannot be placed arbitrarily close to the users because of geographical constraints. In this paper, we quantitatively evaluate this scalability issue in a very densely populated pedestrian street where access points cannot be placed anywhere on the street itself, but only on walls abutting the street. By means of simulations, we obtain the optimal number of access points for a maximum average user throughput and show how this number is affected by user distribution, street width, and beamwidth of the antenna.

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.

Role of altitude when exploring optimal placement of UAV access points

UAVs (Unmanned Aerial Vehicles) are candidates for serving as wireless access points in disaster or mass event scenarios. Here we elaborate on the question where to optimally place the available UAVs in space for a Poisson user distribution on the ground. Since the number of possible placement combinations is too high for a systematic search, we approach the optimal solution by a simple heuristic bio-inspired procedure. It turns out that changes in altitude contribute almost as much to increasing the average spectral efficiency as changes in horizontal directions. However, increasing the altitude requires much more energy than an equal movement in a horizontal direction. We show that restricting altitude movements by an attenuation factor can result in similar results as a procedure without such altitude restrictions. Even more intriguingly, keeping all UAVs at one favorable fixed altitude clearly outperforms the procedure with altitude flexibility. This has implications for the time UAVs can stay aloft with their on-board energy.

Flow-Level Capacity and Performance in HetNets

The deployment of pico cells to cover traffic hot spots within the footprint of a macro cell provides a powerful approach to meet the massive growth in traffic demands fueled by smartphones and bandwidth-hungry applications. Joint optimization of resource allocation and user association is critical to achieve the maximum capacity benefits and performance gains in such heterogeneous network deployments (HetNets). In order to gain insight in the achievable capacity gains, we examine in the present paper the stability and performance of a HetNet system in the presence of flow-level dynamics. The stability condition reveals that in stationary traffic conditions the maximum capacity can be achieved with a static resource split and traffic association rule, provided that these are suitably selected. This suggests that dynamic adaptation on time scales commensurate with the variations in traffic parameters suffices to extract most of the achievable capacity gains. For the case of static cell boundaries and Proportional Fair scheduling, we also present a method for evaluating the flow-level performance in terms of the distribution of the number of active file transfers and expected transfer delay.