Improving Energy Efficiency and Security for Pervasive Computing Systems
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W&M ScholarWorks Dissertations, Theses, and Masters Projects Theses, Dissertations, & Master Projects 2013 Improving Energy Efficiency and Security for Pervasive Computing Systems Fengyuan Xu College of William & Mary - Arts & Sciences Follow this and additional works at: https://scholarworks.wm.edu/etd Part of the Computer Sciences Commons Recommended Citation Xu, Fengyuan, "Improving Energy Efficiency and Security forer P vasive Computing Systems" (2013). Dissertations, Theses, and Masters Projects. Paper 1539623629. https://dx.doi.org/doi:10.21220/s2-z6zn-yv46 This Dissertation is brought to you for free and open access by the Theses, Dissertations, & Master Projects at W&M ScholarWorks. It has been accepted for inclusion in Dissertations, Theses, and Masters Projects by an authorized administrator of W&M ScholarWorks. For more information, please contact [email protected]. Improving Energy Efficiency and Security for Pervasive Computing Systems Fengyuan Xu Zhengzhou, Henan, China Bachelor of Science, Jilin University, 2007 A Dissertation presented to the Graduate Faculty of the College of William and Mary in Candidacy for the Degree of Doctor of Philosophy Department of Computer Science The College of William and Mary August 2013 APPROVAL PAGE This Dissertation is submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Fengyuan Xu Approved by the Committee, August 2013 Committee Chair Associate Professor Qun Li, Computer Science College of William and Mary Professorior EvgervaEvger\|e Smirni, Computer Science College of William and Mary Professor Weizhen Mao, Computer Science College of William and Mary Associate Professor Haining Wang, Computer Science College of William and Mary $LrrnaA. fjosubraU . __________ Senior Researcher Thomas Moscibroda Microsoft Research ABSTRACT Pervasive computing systems are comprised of various personal mobile devices connected by the wireless networks. Pervasive computing systems have gained soaring popularity because of the rapid proliferation of the personal mobile devices. The number of personal mobile devices increased steeply over years and will surpass world population by 2016. However, the fast development of pervasive computing systems is facing two critical issues, energy efficiency and security assurance. Power consumption of personal mobile devices keeps increasing while the battery capacity has been hardly improved over years. At the same time, a lot of private information is stored on and transmitted from personal mobile devices, which are operating in very risky environment. As such, these devices became favorite targets of malicious attacks. Without proper solutions to address these two challenging problems, concerns will keep rising and slow down the advancement of pervasive computing systems. We select smartphones as the representative devices in our energy study because they are popular in pervasive computing systems and their energy problem concerns users the most in comparison with other devices. We start with the analysis of the power usage pattern of internal system activities, and then identify energy bugs for improving energy efficiency. We also investigate into the external communication methods employed on smartphones, such as cellular networks and wireless LANs, to reduce energy overhead on transmissions. As to security, we focus on implantable medical devices (IMDs) that are specialized for medical purposes. Malicious attacks on IMDs may lead to serious damages both in the cyber and physical worlds. Unlike smartphones, simply borrowing existing security solutions does not work on IMDs because of their limited resources and high requirement of accessibility. Thus, we introduce an external device to serve as the security proxy for IMDs and ensure that IMDs remain accessible to save patients' lives in certain emergency situations when security credentials are not available. TABLE OF CONTENTS Acknowledgments v Dedication vi List of Tables vii List of Figures viii 1 Introduction 1 1.1 Energy Modeling on the Smartphone ..................................................... 4 1.2 Improve Energy Consumption of Email S y n c ......................................... 6 1.3 AP Association in Wireless L A N.............................................................. 8 1.4 Secure Wireless Communication in IM D s ............................................... 9 1.5 Organization................................................................................................ 11 2 Smartphone Power Modeling 12 2.1 Background: Power Modeling .................................................................... 15 2.2 Related Work and Motivation .................................................................... 16 2.3 Sensing Current from Battery Voltage D ynam ics .................................. 20 2.3.1 Battery Voltage D yn am ics .............................................................. 20 2.3.2 Reliable Relationship between V-edge and C u rre n t ................... 22 2.3.3 Detecting V -e d g e .............................................................................. 23 2.4 V-edge Energy Measurement S y s te m ..................................................... 26 2.5 Power Modeling Based on V -e d g e ........................................................... 30 2.6 System Design and Implementation ........................................................ 33 2.7 Evaluation ................................................................................................... 36 i 2.7.1 Experimental S etu p .......................................................................... 36 2.7.2 Model Generation T im e .................................................................... 37 2.7.3 Accuracy............................................................................................. 38 2.7.4 System Overhead ............................................................................. 41 2.8 Discussions and Future W ork................................................................... 42 2.9 Conclusions .............................................................................................. 43 3 Optimizing Email Snyc on Smartphones 45 3.1 Background on Email S y n c ...................................................................... 48 3.2 Profiling Energy Cost of Email S y n c ....................................................... 50 3.2.1 Experimental S etu p .......................................................................... 50 3.2.2 Measurement Results .................................................................... 51 3.2.2.1 Stages of receiving an email ............................................ 51 3.2.2.2 Energy cost of receiving an em ail ....................................... 53 3.2.2.3 Energy cost vs. inbox s iz e .................................................. 54 3.2.2.4 Energy cost vs. email s iz e .................................................. 56 3.2.2.5 Network activities in receiving an em ail ........................... 56 3.2.2.6 Storage activities in receiving an e m a il ........................... 58 3.2.2.7 Energy distribution .............................................................. 59 3.2.3 Summary of Findings....................................................................... 60 3.3 Reducing Energy Cost of Email S y n c .................................................... 61 3.3.0.1 Reducing 3G Tail T im e ........................................................ 62 3.3.1 Decoupling Data Transmission from Data Processing............... 65 3.3.2 In-Memory Data Processing ........................................................... 67 3.3.3 Reusing Existing Network Connections ........................................ 69 3.3.4 Data Structure Partitioning .............................................................. 69 3.4 Implementation ............................................................................................ 70 3.5 Evaluation ................................................................................................. 72 ii 3.6 Event Receiving in Other Applications ..................................................... 75 3.7 Related W ork ................................................................................................ 76 3.8 Conclusion................................................................................................... 77 4 Access Point Association in Wireless LAN 84 4.1 Related W ork ................................................................................................ 86 4.2 Motivation...................................................................................................... 88 4.3 Selfish User S tra te g y ................................................................................ 89 4.3.1 Convergence of the Selfish Strategy ........................................... 90 4.3.2 Competitive R a tio ............................................................................. 96 4.4 Online Algorithm .......................................................................................... 97 4.5 Protocol Implementation of SmartAssoc.....................................................107 4.6 Evaluation ......................................................................................................110 4.6.1 Application Aware Probing .................................................................111 4.6.2 Measurement Accuracy ....................................................................112