Browsing by Author "Rahmati, Ahmad"

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    Context for system resource management: An application in wireless data management
    (2008) Rahmati, Ahmad; Zhong, Lin
    Context information brings new opportunities for efficient and effective system resource management of mobile devices. In this work, we focus on the use of context information to manage wireless data. The findings from our field-collected data show that the energy cost of network interfaces poses a great challenge to ubiquitous connectivity, despite fairly good network availability. Based on our findings, we propose to leverage the complementary strengths of Wi-Fi and cellular networks by automatically selecting the more energy-efficient wireless interface based on context information. We formulate the selection of wireless interfaces as a statistical decision problem. The key challenge is to accurately estimate Wi-Fi network conditions without powering up its network interface. We explore the use of different context information, including time, history, cellular network conditions, and device motion, and devise algorithms that can effectively learn from context information and estimate the probability distribution of Wi-Fi network conditions. Simulations based on field-collected traces show that our algorithms can improve the average battery lifetime of a commercial mobile phone for a three-channel ECG reporting application by 39%, very close to the determined theoretical upper bound of 42%. Finally, a field validation of our most simple algorithm demonstrates a 35% battery lifetime improvement in normal usage.
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    Context in Mobile System Design: Characterization, Theory, and Implications
    (2012-09-05) Rahmati, Ahmad; Zhong, Lin; Knightly, Edward W.; Sabharwal, Ashutosh; Kortum, Philip
    Context information brings new opportunities for efficient and effective applications and services on mobile devices. Many existing work exploit the context dependency of mobile usage for specific applications, and show significant, quantified, performance gains by utilizing context. In order to be practical, such works often pay careful attention to the energy and processing costs of context awareness while attempting to maintain reasonable accuracy. These works also have to deal with the challenges of multiple sources of context, which can lead to a sparse training data set. Even with the abundance of such work, quantifying context-dependency and the relationship between context-dependency and performance achievements remains an open problem, and solutions to manage the and challenges of context awareness remain ad-hoc. To this end, this dissertation methodologically quantifies and measures the context dependency of three principal types of mobile usage in a methodological, application agnostic yet practical manner. The three usages are the websites the user visits, the phone numbers they call, and the apps they use, either built-in or obtained by the user from the App Store . While this dissertation measures the context dependency of these three principal types of mobile usage, its methodology can be readily extended to other context-dependent mobile usage and system resources. This dissertation further presents SmartContext, a framework to systematically optimize the energy cost of context awareness by selecting among different context sources, while satisfying the system designer’s cost-accuracy tradeoffs. Finally, this thesis investigates the collective effect of social context on mobile usage, by separating and comparing LiveLab users based on their socioeconomic groups. The analysis and findings are based on usage and context traces collected in real-life settings from 24 iPhone users over a period of one year. This dissertation presents findings regarding the context dependency of three principal types of mobile usage; visited websites, phone calls, and app usage. The methodology and lessons presented here can be readily extended to other forms of context and context-dependent usage and resources. They guide the development of context aware systems, and highlight the challenges and expectations regarding the context dependency of mobile usage.
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    Getting Real: A Naturalistic Methodology for Using Smartphones to Collect Mediated Communications
    (Hindawi Publishing Corporation, 2012) Tossell, Chad C.; Kortum, Philip; Shepard, Clayton W.; Rahmati, Ahmad; Zhong, Lin
    This paper contributes an intentionally naturalistic methodology using smartphone logging technology to study communications in the wild. Smartphone logging can provide tremendous access to communications data from real environments. However, researchers must consider how it is employed to preserve naturalistic behaviors. Nine considerations are presented to this end. We also provide a description of a naturalistic logging approach that has been applied successfully to collecting mediated communications from iPhones. The methodology was designed to intentionally decrease reactivity and resulted in data that were more accurate than self-reports. Example analyses are also provided to show how data collected can be analyzed to establish empirical patterns and identify user differences. Smartphone logging technologies offer flexible capabilities to enhance access to real communications data, but methodologies employing these techniques must be designed appropriately to avoid provoking naturally occurring behaviors. Functionally, this methodology can be applied to establish empirical patterns and test specific hypotheses within the field of HCI research. Topically, this methodology can be applied to domains interested in understanding mediated communications such as mobile content and systems design, teamwork, and social networks.
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    Heterogeneous network access on devices with one or more network interfaces
    (2014-11-04) Nicoara, Angela; Rahmati, Ahmad; Shepard, Clayton; Zhong, Lin; Singh, Jatinder Pal; Deutsche Telekom AG; Rice University; United States Patent and Trademark Office
    A method for managing TCP flows in a mobile device adapted to connect to two or more wireless network types includes enabling connection to a number of networks of different types at the mobile device and executing a plurality of Internet-enabled applications on the mobile device. Each such application forms an existing TCP connection over a first one of the wireless networks. The routing table is modified such that any additional TCP connection will be created on a second one of the wireless networks. The device determines that a termination condition has occurred and in response to determining that the termination condition has occurred, renders an interface on the mobile device to the first one of the wireless networks inoperative.