Veljko Pejovic

Smartphones for Large-Scale Behavior Change Interventions

Equipped with cutting-edge sensing technology and high-end processors, smartphones can unobtrusively sense human behavior and deliver feedback and behavioral therapy. The authors discuss two applications for behavioral monitoring and change and present UBhave, the first holistic platform for large-scale digital behavior change intervention.

Exploiting locality of interest in online social networks

Online Social Networks (OSN) are fun, popular, and socially significant. An integral part of their success is the immense size of their global user base. To provide a consistent service to all users, Facebook, the worlds largest OSN, is heavily dependent on centralized U.S. data centers, which renders service outside of the U.S. sluggish and wasteful of Internet bandwidth. In this paper, we investigate the detailed causes of these two problems and identify mitigation opportunities. Because details of Facebooks service remain proprietary, we treat the OSN as a black box and reverse engineer its operation from publicly available traces. We find that contrary to current wisdom, OSN state is amenable to partitioning and that its fine grained distribution and processing can significantly improve performance without loss in service consistency. Through simulations of reconstructed Facebook traffic over measured Internet paths, we show that user requests can be processed 79% faster and use 91% less bandwidth. We conclude that the partitioning of OSN state is an attractive scaling strategy for Facebook and other OSN services.

Anticipatory Mobile Computing: A Survey of the State of the Art and Research Challenges

Today’s mobile phones are far from the mere communication devices they were 10 years ago. Equipped with sophisticated sensors and advanced computing hardware, phones can be used to infer users’ location, activity, social setting, and more. As devices become increasingly intelligent, their capabilities evolve beyond inferring context to predicting it, and then reasoning and acting upon the predicted context. This article provides an overview of the current state of the art in mobile sensing and context prediction paving the way for full-fledged anticipatory mobile computing. We present a survey of phenomena that mobile phones can infer and predict, and offer a description of machine learning techniques used for such predictions. We then discuss proactive decision making and decision delivery via the user-device feedback loop. Finally, we discuss the challenges and opportunities of anticipatory mobile computing.

My Phone and Me: Understanding People's Receptivity to Mobile Notifications

Notifications are extremely beneficial to users, but they often demand their attention at inappropriate moments. In this paper we present an in-situ study of mobile interruptibility focusing on the effect of cognitive and physical factors on the response time and the disruption perceived from a notification. Through a mixed method of automated smartphone logging and experience sampling we collected 10372 in-the-wild notifications and 474 questionnaire responses on notification perception from 20 users. We found that the response time and the perceived disruption from a notification can be influenced by its presentation, alert type, sender-recipient relationship as well as the type, completion level and complexity of the task in which the user is engaged. We found that even a notification that contains important or useful content can cause disruption. Finally, we observe the substantial role of the psychological traits of the individuals on the response time and the disruption perceived from a notification.

VillageCell: cost effective cellular connectivity in rural areas

Mobile telephony brings clear economic and social benefits to its users. As handsets have become more affordable, ownership has reached staggering numbers, even in the most remote areas of the world. However, network coverage is often lacking in low population densities and low income rural areas of the developing world, where big telecoms often defer from deploying expensive infrastructure. To solve this coverage gap, we propose VillageCell, a low-cost alternative to high-end cell phone networks. VillageCell relies on software defined radios and open-source solutions to provide free local and cheap long-distance communication for remote regions. Our architecture is simple and easy to deploy, yet robust and requires no modification to GSM handsets. Through measuring the call quality metrics and the system capacity under a realistic rural-area network load, we show that VillageCell is indeed an attractive solution for rural area voice connectivity.

Traffic characterization and internet usage in rural Africa

While Internet connectivity has reached a significant part of the worlds population, those living in rural areas of the developing world are still largely disconnected. Recent efforts have provided Internet connectivity to a growing number of remote locations, yet Internet traffic demands cause many of these networks to fail to deliver basic quality of service needed for simple applications. For an in-depth investigation of the problem, we gather and analyze network traces from a rural wireless network in Macha, Zambia. We supplement our analysis with on-site interviews from Macha, Zambia and Dwesa, South Africa, another rural community that hosts a local wireless network. The results reveal that Internet traffic in rural Africa differs significantly from the developed world. We observe dominance of web-based traffic, as opposed to peer-to-peer traffic common in urban areas. Application-wise, online social networks are the most popular, while the majority of bandwidth is consumed by large operating system updates. Our analysis also uncovers numerous network anomalies, such as significant malware traffic. Finally, we find a strong feedback loop between network performance and user behavior. Based on our findings, we conclude with a discussion of new directions in network design that take into account both technical and social factors.

Disease Containment Strategies based on Mobility and Information Dissemination

Human mobility and social structure are at the basis of disease spreading. Disease containment strategies are usually devised from coarse-grained assumptions about human mobility. Cellular networks data, however, provides finer-grained information, not only about how people move, but also about how they communicate. In this paper we analyze the behavior of a large number of individuals in Ivory Coast using cellular network data. We model mobility and communication between individuals by means of an interconnected multiplex structure where each node represents the population in a geographic area (i.e., a sous-préfecture, a third-level administrative region). We present a model that describes how diseases circulate around the country as people move between regions. We extend the model with a concurrent process of relevant information spreading. This process corresponds to people disseminating disease prevention information, e.g., hygiene practices, vaccination campaign notices and other, within their social network. Thus, this process interferes with the epidemic. We then evaluate how restricting the mobility or using preventive information spreading process affects the epidemic. We find that restricting mobility does not delay the occurrence of an endemic state and that an information campaign might be an effective countermeasure.

VillageShare: facilitating content generation and sharing in rural networks

While broadband Internet connectivity has reached a significant part of the worlds population, those living in rural areas of the developing world suffer from poor Internet connectivity over slow long distance links, if they even have connectivity at all. While this has a general negative impact on Internet utilization, our social survey of users in the community of Macha, Zambia shows that the severest impact is in the area of content generation and sharing. To this end, our work describes VillageShare, an integrated time-delayed proxy server and content-sharing Facebook application. Through these two components, VillageShare facilitates localization of traffic, protecting the bandwidth-limited Internet link from content shared between local users, and minimizes upload abortions by time-shifting large uploads to periods when the gateway link is under-utilized. In this work we analyze traffic traces from Macha to discern opportunities for improvement of connection utilization, and then describe and evaluate the VillageShare architecture.

Investigating The Role of Task Engagement in Mobile Interruptibility

Context-awareness of mobile phones is a cornerstone of recent efforts in automatic determination of user interruptibility. Modalities such as a users location, her physical activity, time of day, can be used in machine learning models to infer if a user is going to welcome an incoming notification or not. However, the success of context-aware interruptibility systems questions the existing theory of interruptibility, that is based on the internal state of the user, not her surroundings. In this work we examine the role of a users internal context, defined by her engagement in the current task, on the sentiment towards an interrupting mobile notification. We collect and analyse real-world data on interruptibility of twenty subjects over two weeks, and show that the internal state indeed impacts user interruptibility.

A context-aware approach to wireless transmission adaptation

Recent advancements in wireless transmission have enabled networks with a high level of physical layer flexibility. Unfortunately, these new opportunities are not harnessed by modern wireless systems. Due to inefficient resource allocation, systems typically encounter problems such as spectrum scarcity, energy depletion or low quality of service. In this paper we consider the problem of physical layer parameter adaptation in a flexible wireless system. We observe that for many practical purposes the acceptable quality of communication depends on the interplay among the packet loss ratio, energy savings and spectrum utilization. We harness this fact and propose a context-aware physical layer parameter adaptation solution, WhiteRate. Our solution adjusts the modulation level, coding scheme and channel width to achieve the communication profile that matches application requirements. We implement WhiteRate in GNUradio and evaluate it in both indoor and outdoor environments. We demonstrate improvements on two important fronts: spectrum utilization and energy efficiency. Moreover, we show that by using WhiteRate, both benefits can be achieved simultaneously.