In recent years, the explosion of diverse smart devices such as mobile phones, TVs, watches, and even cars, has completely changed our lives. We communicate with friends through social network services (SNSs) whenever we want, buy stuff without visiting shops, and enjoy multimedia wherever we are, thanks to these devices. However, these smart devices cannot simply interact with each other even though they are right next to each other. For example, when you want to read a PDF stored on a smartphone on a larger TV screen, you need to do complicated work or plug in a bunch of cables. In this paper, we introduce M+, an extension of Android that supports cross-device functionality sharing in a transparent manner. As a platform-level solution, M+ enables unmodified Android applications to utilize not only application functionalities but also system functionalities across devices, as if they were to utilize them inside the same device. In addition to secure connection setup, M+ also allows performing of permission checks for remote applications in the same way as for local. Our experimental results show that M+ enables transparent cross-device sharing for various functionalities and achieves performance close to that of within-device sharing unless a large amount of data is transferred.

Web browsing is a key application on mobile devices. However, mobile browsers are largely optimized for performance, imposing a significant burden on power-hungry mobile devices. In this work, we aim to reduce the energy consumed to load web pages on smartphones, preferably without increasing page load time and compromising user experience. To this end, we first study the internals of web page loading on smartphones and identify its energy-inefficient behaviors. Based on our findings, we then derive general design principles for energy-efficient web page loading, and apply these principles to the open-source Chromium browser and implement our techniques on commercial smartphones. Experimental results show that our techniques are able to achieve a 24.4% average system energy saving for Chromium on a latest-generation big.LITTLE smartphone using WiFi (a 22.5% saving when using 3G), while not increasing average page load time. We also show that our proposed techniques can bring a 10.5% system energy saving on average with a small 1.69\% increase in page load time for mobile Firefox web browser. User study results indicate that such a small increase in page load time is hardly perceivable.

Modern mobile devices are equipped with multiple network interfaces, including 3G/LTE and WiFi. Bandwidth aggregation over LTE and WiFi links offers an attractive opportunity of supporting bandwidth-intensive services, such as high-quality video streaming, on mobile devices. However, achieving effective bandwidth aggregation in mobile environments raises several challenges related to deployment, link heterogeneity, network fluctuation, and energy consumption. We present GreenBag, an energy-efficient bandwidth aggregation middleware that supports real-time data-streaming services over asymmetric wireless links, requiring no modifications to the existing Internet infrastructure and servers. GreenBag employs several techniques, including medium load balancing, efficient segment management, and energy-aware mode control, to resolve such challenges. We implement a prototype of GreenBag on Android-based mobile devices which hosts, to the best knowledge of the authors, the first LTE-enabled bandwidth aggregation prototype for energy-efficient real-time video streaming. Our experiment results in both emulated and real-world environments show that GreenBag not only achieves good bandwidth aggregation to provide QoS in bandwidth-scarce environments but also efficiently saves energy on mobile devices. Moreover, energy-aware GreenBag can minimize video interruption while consuming 14-25% less energy than the non-energy-aware counterpart in real-world experiments.