Scientific Posters

Scientific posters authored by PhD Students and Internship Students from IMDEA Networks will be exhibited during the workshop.

New Methods for Ranking Influence in Social Networks (Download poster 604,3 KB  )
Luis F. Chiroque ^1&2
1 IMDEA Networks Institute, ² Universidad Carlos III de Madrid

Abstract
In this work, propagation dynamics on social networks are studied in order to identify the most influential users. For this purpose, diffusion data has been collected during 4 weeks from a microblogging OSN (online social network) called Tumblr. Then, the propagation graph has been built and studied using the first 2 weeks data (period T1). Subsequently, this graph has been used to predict the influencers during the last 2 weeks (period T2). A ranking of influential nodes is obtained for T2, set as the ground truth. The aim is to predict this ranking using the data from T1. Based on the average spread of users’ posts, rankings obtained with several techniques are tested and compared. These techniques include classical centrality measures used in the literature, the T1 ranking itself, and new alternatives based on effective degree using local (network) information. Whilst all methods perform similarly when considering whole global ranking, differences among them appear when ranking the top influencers. For those, in general, the methods proposed here outperform the classical centrality measures.

Improving the Energy Benefit for 802.3az using Dynamic Coalescing Techniques (Download poster 187 KB  )
Angelos Chatzipapas ^1&2, Vincenzo Mancuso ^1
1 IMDEA Networks Institute, ² Universidad Carlos III de Madrid

Abstract
In this work, we propose a dynamic coalescing algorithm for IEEE 802.3az standard, which dynamically adapts coalescing operations based on the current load and on the delay
experienced in the link. Our results show that our algorithm almost doubles the energy efficiency of EEE with static coalescing while keeping packet delay bounded.

Modeling the Throughput of 1-persistent CSMA in Underwater Networks  (Download poster 810 KB  )
Alain Olivier ¹, Michele Zorzi ¹, Paolo Casari ^2
1 Department of Information Engineering, University of Padova, ² IMDEA Networks Institute

Abstract

The aim of this paper is to present a model for the throughput of the 1-persistent CSMA protocol in underwater net- works, where the typically large propagation delay with respect to the packet transmission time requires to take into account the spatial distribution of the nodes. Our model is developed based on the analysis carried out in [1] for the non-persistent CSMA protocol. Our results show that the 1-persistent CSMA model developed by Tobagi and Kleinrock is still valid as an approximation, with a few small adjustments, even though it considers an equal propagation delay for all pairs of nodes in the network. The proposed model is validated against simulation results based on the network simulator OMNeT++.

Prediction-based Optimization in Mobile Networks (Download poster 886 KB  )
Nicola Bui ^1&2
1 IMDEA Networks Institute, ² Universidad Carlos III de Madrid

Abstract

• Network capacity prediction can be used to prefetch data when signal quality is high and rely on buffered data otherwise
• Imperfect prediction impact
• Multi-user resource optimization
• Admission control
• Evaluation from traces

Collaborative Large-scale Wideband Spectrum Monitoring (Download poster 2MB  )
Roberto Calvo-Palomino^1&2, Domenico Giustiniano¹, Vincent Lenders^3
1 IMDEA Networks Institute, ² Universidad Carlos III de Madrid, ³ Armasuisse, Switzerland

Abstract:

Today's radio frequency (RF) spectrum measurements are mainly performed by governmental agencies which drive around using bulky and expensive specialized hardware. This approach does not scale well, providing us with only a poor situational awareness of the actual RF spectrum usage around us. We propose a large-scale wideband spectrum monitoring system to collaboratively show the spectrum usage over time and frequency. We have developed a monitoring sensor for remote real-time spectrum analysis that builds upon portable and low-cost commercial off-the-shelf
(COTS) hardware components with a total cost per sensor device below $100. Our remote sensing platform is envisioned to be used at larger scale for various applications such as dynamic spectrum access in cognitive radios, detecting regions with elevated electro-smog, or for policy enforcement in the electromagnetic space.

Virtual Wireless Operators: Resource sharing and Statistical multiplexing 
Pablo Caballero^1&2, Albert Banchs², Gustavo de Veciana³, Xavier Perez-Costa^4
1 IMDEA Networks Institute, ² Universidad Carlos III de Madrid, ³ University of Texas at Austin, ⁴ NEC Labs Europe

The traditional model of single ownership of the mobile network infrastructure is being challenged by the forecasted mobile data tsunami and the resulting CAPEX and OPEX costs. In this context, the sharing of network infrastructure among operators has emerged as a way to ensure operators’ future cost competitiveness. While the elementary concepts related to passive network sharing are already being exploited today, active network sharing is raising in importance to enable further reduction of network expenses in a substantial and sustainable way. The work presented addresses this challenge by designing a Multi-Operator Resource Allocation (MORA) framework that allows to flexibly share the RAN resources among multiple virtual operators (tenants). A distributed algorithm that exploits resource allocation and user association is proposed and was benchmarked against other centralized and distributed approaches. A rigorous evaluation of different metrics indicate that this framework significantly outperform legacy solutions.

Beamforming, Interference and Frame Level Protocol Analysis of 60GHz Networks (Download poster 1MB  )
Thomas Nitsche^1&2, Guillermo Bielsa^1&2, Irene Tejado^1&2, Joerg C. Widmer^1
1 IMDEA Networks Institute, ² Universidad Carlos III de Madrid

Millimeter wave communication for wireless local area networks is rapidly gaining importance, promising extremely high data rates and spatial frequency reuse in dense networks. Despite the fact that devices following the WiHD and WiGig standard have been commercially available for a few years, thorough studies of their performance and in particular the beamforming mechanisms and directional communication schemes in realistic wireless settings are lacking. Very similar mechanisms are used in upcoming devices based on the IEEE 802.11ad standard and understanding them well is crucial for the design and simulation of next generation millimeter wave networks.

We present, to our knowledge, the first in-depth beam forming, interference and frame level protocol analysis of off-the-shelf millimeter wave systems with phased antenna arrays. Our study focuses particularly on the relation between beam patterns and resilience against interference. While millimeter wave communication is commonly believed to be widely interference free, we find strong side lobes in the measured beam patterns that can invalidate this assumption. Further, we observe weak directionality when beam forming towards the boundary of the transmission area of an antenna array, which further intensifies interference effects. Finally, we evaluate the effects of inter-platform interference for joint deployments of commercial systems following different communication protocols.

Optimizing in-band underlay D2D transmissions (Download poster 645KB  )
Christian Vitale^1&2, Vincenzo Mancuso¹, Gianluca Rizzo^3
1 IMDEA Networks Institute, ² Universidad Carlos III de Madrid, ³ HES SO Valais

Also in cellular networks, D2D communications provide numerous advantages. Nevertheless, modelling D2D systems remains a complex and unsolved task. In this work, we present the first analytical study on D2D system performance. Our approach models interdependencies among D2D and cellular transmitters in details and achieves a conservative estimation of the stability region of D2D systems, as well as evaluates the effects of D2D transmissions on cellular users. Furthermore, the proposed approach can easily tradeoff performances for less complexity in a realistic application, i.e., in a proportional fairness optimization.

Passive mobile bandwidth classification based on short lived TCP connections 
Foivos Michelinakis^1,2, Gunnar Kreitz³, Riccardo Petrocco³, Boxun Zhang³, Joerg Widmer^1
1 IMDEA Networks Institute, ² Universidad Carlos III de Madrid, ³ Spotify

The majority of connections on the mobile Internet are short lived TCP connections which spend a significant portion of the data exchange within the slow start phase. We propose a tool that estimates the bandwidth class a mobile device is currently operating in. Not only does our solution achieve good precision even if only the first few packets of a TCP connection are available, but its confidence improves for larger flows. The estimate takes into consideration artifacts introduced by the slow start behavior of TCP, the mobile scheduler and the phone hardware. Existing bandwidth measurement tools do not achieve the same reliability of our technique when used on short lived TCP connections. We have tested our solution on traces collected in 4 European countries.
Since our tool obtains bandwidth estimates even when the device is lightly used, it enables Quality-of-Service in media streaming and resource optimization algorithms.

Opportunistic Timing Signals for Pervasive Localization (Download poster 1MB  )
Aymen Fakhreddine^1,2, Domenico Giustiniano¹, Vincent Lenders^3
1 IMDEA Networks Institute, ² Universidad Carlos III de Madrid, ³ Armasuisse

As GPS, a time based satellite navigation system, performs poorly in indoor areas and urban canyons, we aim to take advantage of timing signals available in terrestrial wireless technologies to improve the positioning accuracy achieved with GPS and be able to compute the mobile device position when GPS fails to do so. We seek a solution that extends timing-based positioning beyond GPS and runs at the level of the mobile device. For this work we consider localization with GPS complemented with WiFi Time-of-Flight (ToF) as WiFi is largely deployed in indoor areas. Our solution requires only timing information from commercial off-the-shelf WiFi chipsets without any additional hardware or standard changing. We propose a multi-technologies multilateration positioning based on the Extended Kalman filter for heterogeneous data fusion and we show that it performs better than pure GPS solutions.

You can access last year’s posters here.