E. de Lara

Are GSM Phones THE Solution for Localization

In this paper, we argue that localization solution based on cellular phone technology, specifically GSM phones, is a sufficient and attractive option in terms of coverage and accuracy for a wide range of indoor, outdoor, and placebased location-aware applications. We present preliminary results that indicate that GSM-based localization systems have the potential to detect the places that people visit in their everyday lives, and can achieve median localization accuracies of 5 and 75 meters for indoor and outdoor environments, respectively.

User mobility for opportunistic ad-hoc networking

As mobile devices become increasingly pervasive and commonly equipped with short-range radio capabilities, we observe that it might be possible to build a network based only on pair-wise contact of users. By using user mobility as a network transport mechanism, devices can intelligently route latency-insensitive packets using power-efficient short-range radio. Such a network could provide communication capability where no network infrastructure exists, or extend the reach of established infrastructure. To collect user mobility data, we ran two user studies by giving instrumented PDA devices to groups of students to carry for several weeks. We evaluate our work by providing empirical data that suggests that it is possible to make intelligent routing decisions based on only pair-wise contact, without previous knowledge of the mobility model or location information.

The SkyLoc Floor Localization System

When a mobile user dials 911, a key to arriving to the emergency scene promptly is knowing the location of the mobile user. This paper presents SkyLoc, a GSM fingerprinting-based localization system that runs on a mobile phone and identifies the current floor of a user in tall multi-floor buildings. Knowing the floor in a tall building significantly reduces the area that emergency service personnel have to canvas to locate the individuals in need. We evaluated our system in three multi-floor buildings located in Washington DC, Seattle and Toronto. Our system identifies the floor correctly in up to 73% of the cases and is within 2 floors in 97% of the cases. The system is robust as it works for different network operators, when the training and testing sets were collected with different hardware and up to one month apart. In addition, we show that feature selection techniques that select a subset of highly relevant radio sources for fingerprint matching nearly double the localization accuracy of our system

A cross-layer approach to service discovery and selection in MANETs

When a service is offered by multiple servers in a mobile ad hoc network (MANETs), the manner in which clients and servers are paired together, referred to as service selection, is crucial to network performance. Good service selection groups clients with nearby servers, localizing communication, which in turn reduces inter-node interference and allows for multiple concurrent transmissions in different parts of the network. Although much previous research has concentrated on service discovery in MANETs, not much effort has gone into understanding the effects of service selection. This paper demonstrates that service selection in MANETs has profound implications for network performance. Specifically, we show that effective service selection can improve network throughput by up to 400%. We show that to maximize performance service selection decisions need to be continuously reassessed to offset the effects of topology changes. We argue that effective service selection in MANETs requires a cross-layer approach that integrates service discovery and selection functionality with network ad hoc routing mechanisms. The cross-layer approach leverages existing routing traffic and allows clients to switch to better servers as network topology changes

Simplified simulation models for indoor MANET evaluation are not robust

We evaluate the robustness of simplified mobility and radio propagation models for indoor MANET simulations. A robust simplification allows researchers to extrapolate simulation results and reach reliable conclusions about the expected performance of protocols in real life. We show that common simplified mobility and radio propagation models are not robust. Experiments with DSR and DSDV, two representative MANET routing protocols, show that the simplifications affect the two protocols in very different manners. Even for a single protocol, the effects on perceived performance can vary erratically as parameters change. These results cast doubt on the soundness of evaluations of MANET routing protocols based on simplified mobility and radio propagation models, and expose the urgent need for more research on realistic MANET simulation.

An Empirical Evaluation of the Student-Net Delay Tolerant Network

Radio equipped mobile devices have enjoyed tremendous growth in the past few years. We observe that in the near future it might be possible to build a network that routes delay-tolerant packets by harnessing user mobility and the pervasive availability of wireless devices. Such a delay-tolerant network could be used to supplement wireless infrastructure or provide service where none is available. Since mobile devices in a delay-tolerant network forward packets to nearby users, the devices can use short-range radio, which potentially reduces device power consumption and radio contention. The design of a user mobility based delay-tolerant network raises two key challenges: determining the connectivity of such a network, and determining the latency characteristics and replication requirements of routing algorithms in such a network. To determine realistic contact patterns, we collected user mobility data by conducting two user studies. We outfitted groups of students with instrumented wireless-enabled PDAs that logged pairwise contacts between study participants over a period of several weeks. Experiments conducted on these traces show that it is possible to form a delay-tolerant network based on human mobility. The network has good connectivity, so that routes exist between almost all study participants via some multi-hop path. Moreover, it is possible to effectively route packets with modest replication

Community-driven adaptation: automatic content adaptation in pervasive environments

Mobile devices are increasingly being used to access Web content but lack the resources for proper presentation to the user. To address this problem, content is typically adapted to be more suitable for a mobile environment. Community-driven adaptation (CDA) is a novel approach to automatic content adaptation for mobile devices that adapts content based on feedback from users. CDA groups users into communities based on common characteristics, and assumes that users of the same community have similar adaptation requirements. CDA learns how to adapt content by observing how members of a community alter adapted content to make it more useful to them. Experiments that consider the idealized case, where all users perform the same task, show that CDA can reduce wastage of network bandwidth by up to 90% and requires less user interaction to correct bad adaptation decisions compared with existing approaches to automatic content adaptation.

Enabling Secure and Spontaneous Communication between Mobile Devices using Common Radio Environment

With the proliferation of mobile devices, spontaneous interactions between co-located devices that do not know each other a priori will become commonplace. Securing these interactions against eavesdropping and man-in-the-middle attacks is an important and challenging task. In this paper, we postulate that mobile devices that are positioned in close proximity may be able to derive a shared secret to secure their communication by monitoring fluctuations in the signal strength of existing ambient radio sources (GSM cell towers or WiFi access points) in their common environment. We explore the feasibility of deriving location-based secrets and describe two approaches for how such a secret could be used to secure spontaneous communication. Deriving location-based secrets is a hard problem because while the radio environment perceived by various devices in close proximity is similar, it is not identical.

Real-World Ubicomp Deployments: Lessons Learned

Among the many branches of computer science, ubiquitous computing enjoys an unusually distinguished history of creating and deploying prototypes. Why is this? A tempting answer is that many ubicomp researchers and practitioners have backgrounds in subjects such as HCI and systems--areas with a strong focus on learning from deploying working prototypes. However, a more compelling answer might be that ubicomp, unlike almost every other subspecialty with the exception of HCI, is about embedding computing into existing human systems. This introduction is part of a special issue on Real-World Deployments.

Iterative adaptation for mobile clients using existing APIs

Iterative adaptation is a novel approach to adaptation for resource-limited mobile and wireless environments that supports powerful application-specific adaptations without requiring modifications to the applications source code. Common productivity applications, such as browsers, word processors, and presentation tools, export APIs that allow external applications to control their operation. The novel premise in iterative adaptation is that these APIs are sufficient to support a wide range of adaptation policies for applications running on resource-limited devices. In addition to allowing adaptation without having to change the applications source code, this approach has a unique combination of advantages. First, it supports centralized management of resources across multiple applications. Second, it makes it possible to modify application behavior after the application has been deployed. This paper evaluates the extent to which existing APIs can be used for the purposes of adapting document-based applications to run on bandwidth-limited devices. In particular, we implement a large number of bandwidth adaptations for applications from the Microsoft Office and the OpenOffice productivity suites and for Internet Explorer. Although we find limitations in their APIs, we are able to implement many adaptation policies without much complexity and with good performance. Moreover, iterative adaptation achieves performance similar to an approach that implements adaptation by modifying the application, while requiring only a fraction of the coding effort.