Mobile Systems Interest Group Seminars

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Upcoming Seminars:

Seminar time: Tuesdays from 2pm to 3pm
Location: room 6.12 MPEB

14 October 2008 2pm MPEB 6.12
Speaker: The MobiSys Group

Title: Brainstorming and Update Session

Abstract:
We would like to start this year's seminar series with a group presentation. A few people have left and a few others have joined us, so we'd like each member of the group to introduce her/him self and their research work to the rest of us. This is an opportunity to get to know our work and research interests better, and possibly kick off some useful discussions and collaborations!

Format: 4 slides max: scenario/problem (1), complication/proposals (2), and future work (1). Find a template here, and an example slide set here.

21 October 2008 2pm Foster Court 216
Speaker: Daniele Quercia

Title: Sharing Mobile Content With Trust

Abstract:
Using mobile phones, people may create and distribute different types of digital content (e.g., photos, videos). Then, to avoid content overload, they need to locate quality content. They may do so by having their phones exchange ratings with each other. I will talk about how mobile phones store ratings in a secure way*, and how they use those ratings for locating quality content^.

* MobiRate: Making Mobile Raters Stick to their Word. Ubicomp 2008. ACM. [paper]

^ Lightweight Distributed Trust Propagation. ICDM 2007. [paper]

28 October 2008 2pm Foster Court 216
Speaker: Sonia Ben Mokhtar

Title: TBA

Abstract:
TBA

4 November 2008 2pm MPEB 6.12
Speaker: Neal Lathia

Title: TBA

Abstract:
TBA

Past Seminars:

22 July 2008 2pm 6.12
Speaker: Lu Yan

Title: Using Game Theory in Cooperative and Relay Communications for Wireless Ad hoc Networks

Abstract:
Within the rising communication paradigm of 4G, novel types of cooperation emerge. Instead of conventional selfish point-to-point communications, 4G will support cooperative communication strategies by establishing ad-hoc connectivity among spatially proximate users. While initial technical research efforts have started and demonstrated a potential boost in terms of quality of service delivery, the foundation of cooperation in wireless ad hoc networks is still largely unexplored. Every node in these networks is both end host (it generates its own data and routing traffic) and infrastructure (it forwards traffic for others), but rational nodes have no incentive to cooperatively forward traffic for others, since this kind of forwarding is not costless. In this talk, we use game theory to analyze cooperative mechanisms, and derive optimal criteria in forwarding. Distinguished from existing works in the computer science literature, our approach takes the consideration of realistic scenarios such as noise, non-simultaneously, non-perfect measurement, and different strategies by the nodes. In addition, we reflect the relationship between game theory and trust/reputation, and pros and cons of game theory itself.

15 July 2008 2pm 6.12
Speaker: Valentina Zanardi

Title: Social Ranking: Uncovering Relevant Content Using Tag-based Recommender Systems

Abstract:
Social (or folksonomic) tagging has become a very popular way to describe, categorise, search, discover and navigate content within Web 2.0 websites. Unlike taxonomies, which overimpose a hierarchical categorisation of content, folksonomies empower end users by enabling them to freely create and choose the categories (in this case, tags) that best describe some content. However, as tags are informally defined, continually changing, and ungoverned, social tagging has often been criticised for lowering, rather than increasing, the efficiency of searching, due to the number of synonyms, homonyms, polysemy, as well as the heterogeneity of users and the noise they introduce. In this paper, we propose Social Ranking, a method that exploits recommender system techniques to increase the efficiency of searches within Web 2.0. We measure users' similarity based on their past tag activity. We infer tags' relationships based on their association to content. We then propose a mechanism to answer a user's query that ranks (recommends) content based on the inferred semantic distance of the query to the tags associated to such content, weighted by the similarity of the querying user to the users who created those tags. A thorough evaluation conducted on the CiteULike dataset demonstrates that Social Ranking neatly improves coverage, while not compromising on accuracy.

8 July 2008 2pm 6.12
Speaker: Afra Mashhadi

Title: Coping with unwanted content in MANets

Abstract:
The advent of the Internet has enabled the worldwide distribution of digital content (e.g., news, music, pictures, etc.) at almost zero cost. It is anticipated that, in the near future, digital content will be increasingly created and distributed over delay-tolerant mobile ad-hoc networks. Delay-tolerant network protocols, based on a store-and-forward mechanism, have been developed to enable communication in scenarios where end-to-end connectivity cannot be assumed. However, they have mainly focused on unicast communication, while digital content distribution calls for a many-to-many communication style, where producers and consumers are sharply decoupled, both in time and space.

We believe to avoid nodes getting overwhelmed with unrelated content, a smart overlay is needed to involve least number of non-interested nodes while delivering information to interested people. We believe reasoning about nodes' mobility patterns and nodes' cooperation can achieve high delivery rates, without causing significant overhead.

In this talk we present our initial ideas and pre analysis results.

2 July 2008 2pm 6.12
Speaker: Christian Wallenta

Title: Analysing and Modelling Traffic of Systems with Highly Dynamic User Generated Content

Abstract:
As the web continues to evolve, its users have gone from only consuming content to actually producing it, resulting in systems with highly dynamic, user-generated content that cannot be easily modelled with existing tools. In this paper we investigate two such systems, digg and reddit, derive a general model for them, and show how this model can be used to improve their efficiency as well as that of other systems with similar characteristics.

In order to achieve this, we have collected data on hundreds of thousands of posts and member profiles from both sites. Digg and reddit are social news sites that allow users to post links to other websites as well as to vote for them. We analyse the data to get an understanding of how content is generated and how the popularity of a post evolves over time. We use the results of this analysis coupled with user-location information to derive a general model that describes the user posting behaviour across different time zones.

We further demonstrate how this model can be used to do efficient replication and caching, improving these systems' performance. More importantly though, the periodic trends inherent in the model are not only applicable to these news sites, but also to applications as varied as chatting and online gaming servers, peer-to-peer content distribution and energy-efficient load balancing. We end by showing how the derived model can be used to improve some of these systems.

24 June 2008 2pm 6.12
Speaker: Daniele Quercia

Title: MobiRate: Making Mobile Raters Stick to their Word

Abstract:
To share services, mobile devices may need to locate reputable in-range providers and, to do so, they may exchange ratings with each other. However, providers may well tweak ratings to their own advantage. That is why we have designed a new decentralized mechanism (dubbed MobiRate) with which mobile devices store ratings in (local) tamper-evident tables and check the integrity of those tables through a gossiping protocol. We evaluate the extent to which MobiRate reduces the impact of tampered ratings and consequently locates reputable service providers. We do so using real mobility and social network data. We also assess computational and communication costs of MobiRate on mobile phones.

17 June 2008 2pm 6.12
Speaker: Anders Lindgren

Title: Phase Transitions of Opportunistic Communication

Abstract:
In this paper, we study the utility of opportunistic communication systems with the co-existence of network infrastructure. We study how some important performance metrics change with varying degrees of infrastructure and mobile nodes willing to participate in the opportunistic forwarding. In doing so, we observe phase transitions in the utility of infrastructure and opportunistic forwarding respectively at different points in the design space. We discuss the implications that this has for the design of future network deployments and how this observation can be used to improve network performance, while keeping cost at a minimum.

3 June 2008 2pm 6.12
Speaker: Panteha Saeedi

Title: Self-Organized Multi-agent System: Hierarchical Hybrid Path-Planning for Time Critical Missions

Abstract:
Autonomous multi-robot systems perform inadequately in time critical missions, while they tend to explore exhaustively each location of the field in one phase. This work is aiming to solve this problem by introducing hierarchy of exploration strategies. Agents explore an unknown search terrain with complex topology in multiple predefined stages. Hybrid path planning algorithm generates specific search strategy for each stage. Our simulations have been performed on different environments in which the complexity of the search field has been defined by the shape and number of obstacles. The results show that a hierarchy of exploration strategies minimizes the exploration time while maximizing the exploration area by learning the search field independent from its complexity.

27 May 2008 2pm 6.12
Speaker: Arianna Bassoli

Title: Social Urban Computing

Abstract:
In this lecture I will present my work in the area of ubiquitous and urban computing design. Starting from the approach used Ð social computing Ð which values the adoption of social science methods for informing design, I will move on to describe some of the mobile peer-to-peer applications I created: including an application allowing users to tune in to the music that other people around them are listening to, and a much larger scale system for sharing music on, in, and through the London Underground.

13 May 2008 2pm 6.12
Speaker: Ettore Ferranti

Title: Robot-Assisted Discovery of Evacuation Routes in Emergency Scenarios

Abstract:
When an emergency occurs within a building, it is crucial to guide victims towards emergency exits or human responders towards the locations of victims and hazards. The objective of this work is thus to devise distributed algorithms that allow agents to dynamically discover and maintain short evacuation routes connecting emergency exits to critical cells in the area. We propose two Evacuation Route Discovery mechanisms, Agent2Tag-ERD and Tag2Tag-ERD, and show how they can be seamlessly integrated with existing exploration algorithms, like Ants, MDFS and Brick&Mortar. We then examine the interplay between the tasks of area exploration and evacuation route discovery; our goal is to assess whether the exploration algorithm influences the length of evacuation paths and the time that they are first discovered. Finally, we perform an extensive simulation to assess the impact of the area topology on the quality of discovered evacuation paths.

6 May 2008 2pm 6.12
Speaker: Doina Bucur

Title: Modelling and Verification for Context Awareness

Abstract:
Models and model verification help investigate the basic concepts upon building adaptive and scalable ubiquitous systems. We provide a simple process calculus based on Mobile Ambients to model services and their provision and discovery in mobile systems, either fully ad hoc or served by an infrastructure. We easily express contextual commands (i.e., commands from a node which behave differently according to the node's current context) and context-triggered actions (i.e., actions sprouted on a node by a certain configuration of the context). We then give sample encodings in this model of real systems. Finally, we show a type system for proving by conservative over-approximation the satisfiability of firewalls distributed over such mobile networks. In the process, we review the techniques for an effective verification procedure over a large state space system. Joint work with Mogens Nielsen, University of Aarhus, Denmark.

22 April 2008 2pm 6.12
Speaker: Christoforos Anagnostopoulos and Dimitris Tasoulis

Title: Joint talk on adaptive filtering in real-time environments: handling delayed data and online sensor selection

Abstract:
The advent of real-time monitoring and data collection techniques, such as mobile sensor networks, poses novel challenges to statistical theory. Models must constantly adapt to accomodate incoming data and remain robust to occasional disruptions in communication. In this presentation, we address two essential difficulties: how to handle delayed observations and how to optimally select which sensors to query at each timepoint --- in both cases, trading off estimation accuracy against communication bandwidth and power consumption.

Part I: A number of procedures have been proposed to handle delayed observations. A common characteristic of these methods is the policy of always incorporating, or fusing, delayed measurements at the time they are finally available. In this presentation, we show how to relax this procedure and fuse measurements selectively via thresholding techniques. Using a collaborative signal processing scenario we explicitly compare delayed and undelayed information, by using a-priori estimations of individual measurements' utility. Without using additional communication steps we can achieve significant performance improvement compared to simply discarding delayed measurements.

Part II: Existing variable selection methods are all reliant on the assumptions that the data are sampled off-line, from a static correlation structure. In this talk we will demonstrate how these constraints may be relaxed to accomodate streaming data, via online optimization techniques. We observe that performance is still critically dependent on the speed at which we "forget" past datapoints, as well as the number of sensors queried per tick. We propose online self-tuning techniques for adapting these parameters to the data, with promising results that raise interesting questions about the nature of learning in dynamic environments.

15 April 2008 2pm 6.12
Speaker: Leonardo Mostarda

Title: GOANNA: State machine monitors for distributed applications

Abstract:
Today's increasing complexity and ubiquitous nature of software systems brings out new challenges for building monitoring systems. Applications are increasingly composed of a large number of distributed mobile components that run in heterogeneous devices and do not rely on a fixed infrastructure. In such as complex scenario different components can misbehave independently at the same time. This misbehave detection can require correlation of events scattered over several components and recovery can affect different distributed components. These challenges have led researchers to recognize the need for new monitoring approaches. In particular, modern monitoring systems should be able to: (i) correlate information from different sources; (ii) scale; (iii) quickly detect misbehavior; (iv) allow the monitoring of decentralized applications; (v) provide different functionalities (e.g., logging, testing, dependability and security). In this talk we present our prototype system that allows the generation of decentralized monitoring systems for ubiquitous applications. We provide a monitoring definition language to describe both the system model and the monitoring system definition, i.e., events to be monitored, an event interpretation specification (a set of FSMs) and reaction policies. We validate our approach in a sensor based application.

8 April 2008 2pm 6.12
Speaker: Antonios Skordylis

Title: Delay-bounded Routing in Vehicular Ad-hoc Networks

Abstract:
Ad hoc networks formed by travelling vehicles are envisaged to become a common platform that will support a wide variety of applications, ranging from road safety to advertising and entertainment. The multitude of vehicular applications calls for routing schemes that satisfy user-defined delay requirements while at the same time maintaining a low level of channel utilization to allow their coexistence. Our work focuses on the development of carry-and-forward schemes that attempt to deliver data from vehicles to fixed infrastructure nodes in an urban setting. The proposed algorithms leverage local or global knowledge of traffic statistics to carefully alternate between the Data Muling and Multihop Forwarding strategies, in order to minimize communication overhead while adhering to delay constraints imposed by the application. We evaluate our schemes using realistic vehicular traces on a real city map.

4 March 2008 2pm 6.12
Speaker: Tassos Noulas

Title: COWARD: COntact-aWAre Routing for Delay tolerant networking

Abstract:
Social interaction of people through their devices are becoming more and more common as new devices enable decentralized peer to peer interaction. Messages can be exchanged directly when people meet or can be carried by people which have regular meeting patterns with the interested receivers of messages. Many approaches to the so called opportunistic information dissemination have emerged in recent years, starting from epidemic style protocols, which however have high overhead. The research community has then appealed to alternative approaches that intelligently exploit contact patterns information. In this paper, we introduce COWARD, a link state protocol, where link weights are defined by means of a statistical estimation of the inter-contact times between a pair of hosts. Relying on this metric, our protocol discovers the shortest paths to different destinations in the network and is able to exploit multiple paths in order to forward messages in a more reliable manner. We evaluate the approach on three different human mobility trace sets. In addition, we compare the performance of COWARD with three other protocols, namely Spray and Wait, Student-Net and Epidemic.

26 February 2008 2pm 6.12
Speaker: Claudio Baccigalupo

Title: Poolcasting - a Social Web Radio for Group Customisation

Abstract:
Poolcasting is a social Web radio architecture where the group of listeners is able to influence in real time the music played on each channel. Participants contribute to the radio with songs they own, create radio channels and evaluate the proposed music, while an automatic intelligent technique is in charge of scheduling each channel with a group-customised smooth sequence of songs. One issue Poolcasting has to deal with is musical: how to generate "smooth" sequences, in which each song is musically associated with the song it follows, as it normally occurs in terrestrial radio programs. For this purpose, Poolcasting employs musical knowledge coming from the analysis of playlists retrieved from the Web. Another issue Poolcasting faces is social: how to aggregate the preferences of different listeners and make everyone satisfied on the long run. For this purpose, Poolcasting opts for an approach that promotes fairness among listeners with diverging preferences.

19 February 2008 2pm 6.12
Speaker: Maziar Nekovee

Title: Modelling Wireless Epidemics

Abstract:
I use a combination of large-scale simulations and mathematical modelling to study wireless worm epidemics in both fixed and mobile wireless adhoc networks. These studies show that the spreading of worms in fixed adhoc networks is greatly affected by a combination of spatial correlations arising from the network topology and temporal correlations resulting form the medium access control. Neither standard mass action models from mathematical biology, which are widely used to model Internet epidemics, nor their recent extensions to include network effects are capable of capturing these correlations. However, spatial epidemic models provide a promising alternative. On the other hand, in the case of mobile adhoc networks I show that worm spreading can be described by mass action equations, provided device mobility is self-consistently incorporated in these equations.

5 February 2008 2pm 6.12
Speaker: Luca Mottola

Title: Logical Neighborhoods: Programming Wireless Sensor Networks (One Slice at a Time)

Abstract:
In a recent report, market research firm ONWorld predicts that the global market for wireless sensor networks (WSNs) will grow tenfold by 2011. Simultaneously, ONWorld also identifies ease of programming as the major barrier for a widespread adoption of WSNs. As modern WSNs increasingly become decentralized and heterogeneous, the provision of high-level, yet efficient programming abstractions will play a major role in the near future. In this talk, we present our work on Logical Neighborhoods, a programming abstraction enabling a higher-level notion of proximity in WSN programming. By redefining the traditional notion of physical neighborhood, Logical Neighborhoods empower programmers with the ability to slice the network based on application requirements. Developers can leverage off Logical Neighborhoods directly, or build higher-level abstractions on top. During the talk, we illustrate our investigations in both directions, exploring the use of Logical Neighborhoods in settings from software reconfiguration to sensor network macro-programming.

29 January 2008 2pm 6.12
Speaker: Adriano Galati

Title: TMobile Networks Parameters and Ideal Gas Law for mobile ad-hoc networks

Abstract:
In this talk we discuss some network parameters such as Contacts Surface and Contacts Volume and characterise Contact-Time and InterContact-Time in terms of Network Entropy. We also draw attention to an isomorphism between the Ideal Gas Law (pV=nRT) and network behaviour (equation of state for mobile ad-hoc networks) which can be exploited for traffic congestion management and network monitoring in MANet/DTN.

• MobiSys 2007
• MobiSys 2006 and before

This page was last modified 25/06/07